audit pass 9: XSS fix, focus management, ARIA labels, and :focus-visible gaps

JS:
- Lightbox: remove keydown listener on close (memory leak fix)
- Lightbox: restore focus to trigger on close
- Right drawer: fix aria-hidden="false" anti-pattern to removeAttribute
- Markdown renderer: block javascript:/data: protocol URIs in link and
  image replacements to prevent XSS
- Sidebar submenus: add aria-expanded tracking on toggle; hide decorative
  chevron from screen readers; initialize aria-expanded on mount

CSS:
- Add :focus-visible to .lt-sidebar-toggle (interactive button)
- Add :focus-visible to .lt-dropzone (focusable container)
- Fix .lt-stat-card:focus-visible outline-offset to -2px (clip-path clips it)
- Add light theme override for .lt-nav-drawer-link:focus-visible
- Adjust .lt-split-divider:focus-visible outline-offset to 3px

HTML:
- Range input: update aria-valuenow dynamically on input event
- Combobox label: add for="demo-combobox-input" association
- Typeahead label: add for="demo-typeahead-input" association
- Dropzone file input: add aria-label
- Notification items: add descriptive aria-label to all 4 items;
  add aria-hidden="true" to decorative dot spans
- Mark all read button: add type="button" to prevent accidental form submit

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

base.css

@@ -1425,6 +1425,7 @@ select option:checked {
   transition: var(--transition-fast);
 }
 .lt-sidebar-toggle:hover { color: var(--accent-cyan); text-shadow: var(--glow-cyan); }
+.lt-sidebar-toggle:focus-visible { outline: 2px solid var(--accent-cyan); outline-offset: 2px; border-radius: 2px; }
 
 .lt-sidebar-body { padding: var(--space-md); }
 
@@ -1502,7 +1503,7 @@ select option:checked {
   border-color: var(--accent-cyan-border);
   box-shadow: var(--box-glow-cyan);
 }
-.lt-stat-card:focus-visible { outline: 2px solid var(--accent-cyan); outline-offset: 2px; }
+.lt-stat-card:focus-visible { outline: 2px solid var(--accent-cyan); outline-offset: -2px; }
 .lt-stat-card:hover::before,
 .lt-stat-card.active::before { height: 100%; }
 
@@ -2774,6 +2775,7 @@ input[type="range"].lt-range::-moz-range-thumb {
   position: relative;
   clip-path: polygon(0 0, calc(100% - 16px) 0, 100% 16px, 100% 100%, 16px 100%, 0 calc(100% - 16px));
 }
+.lt-dropzone:focus-visible { outline: 2px solid var(--accent-cyan); outline-offset: -2px; }
 .lt-dropzone:hover,
 .lt-dropzone.drag-over {
   border-color: var(--accent-cyan);
@@ -3619,6 +3621,7 @@ html[data-theme="light"] .lt-nav-link.active        { color: var(--accent-orange
 html[data-theme="light"] .lt-nav-drawer-link        { color: var(--text-secondary); }
 html[data-theme="light"] .lt-nav-drawer-link:hover  { background: var(--accent-cyan-dim); color: var(--accent-cyan); }
 html[data-theme="light"] .lt-nav-drawer-link.active { color: var(--accent-orange); background: var(--accent-orange-dim); }
+html[data-theme="light"] .lt-nav-drawer-link:focus-visible { outline: none; color: var(--accent-cyan); background: var(--accent-cyan-dim); box-shadow: inset 3px 0 0 var(--accent-cyan); }
 html[data-theme="light"] .lt-sidebar-nav-link        { color: var(--text-secondary); }
 html[data-theme="light"] .lt-sidebar-nav-link:hover  { background: var(--accent-cyan-dim); }
 html[data-theme="light"] .lt-sidebar-nav-link.active { background: var(--accent-orange-dim); color: var(--accent-orange); }
@@ -4522,7 +4525,7 @@ body.lt-is-offline .lt-main { margin-top: 2rem; transition: margin-top 0.25s eas
 }
 .lt-split-divider:hover,
 .lt-split-divider.is-dragging { background: var(--accent-cyan); }
-.lt-split-divider:focus-visible { outline: 2px solid var(--accent-cyan); outline-offset: 2px; }
+.lt-split-divider:focus-visible { outline: 2px solid var(--accent-cyan); outline-offset: 3px; }
 .lt-split--vertical .lt-split-divider::before { top: -6px; bottom: -6px; left: 0; right: 0; cursor: row-resize; }
 .lt-split--vertical .lt-split-divider { cursor: row-resize; }
 /* On mobile, stack vertically and hide divider */

base.html

@@ -126,32 +126,32 @@
         <div class="lt-notif-panel" id="lt-notif-panel" role="region" aria-label="Notifications" aria-hidden="true">
           <div class="lt-notif-panel-header">
             <span>Notifications</span>
-            <button class="lt-notif-panel-clear" id="lt-notif-clear-all">Mark all read</button>
+            <button type="button" class="lt-notif-panel-clear" id="lt-notif-clear-all">Mark all read</button>
           </div>
           <div class="lt-notif-panel-list">
-            <div class="lt-notif-item lt-notif-item--unread" role="button" tabindex="0">
-              <span class="lt-notif-dot"></span>
+            <div class="lt-notif-item lt-notif-item--unread" role="button" tabindex="0" aria-label="Unread: P1 alert: storage link-down, 5 min ago. Press Enter to dismiss.">
+              <span class="lt-notif-dot" aria-hidden="true"></span>
               <div class="lt-notif-item-body">
                 <div class="lt-notif-item-title">P1 alert: storage link-down</div>
                 <div class="lt-notif-item-time">5 min ago</div>
               </div>
             </div>
-            <div class="lt-notif-item lt-notif-item--unread" role="button" tabindex="0">
-              <span class="lt-notif-dot"></span>
+            <div class="lt-notif-item lt-notif-item--unread" role="button" tabindex="0" aria-label="Unread: Worker node-03 reconnected, 12 min ago. Press Enter to dismiss.">
+              <span class="lt-notif-dot" aria-hidden="true"></span>
               <div class="lt-notif-item-body">
                 <div class="lt-notif-item-title">Worker node-03 reconnected</div>
                 <div class="lt-notif-item-time">12 min ago</div>
               </div>
             </div>
-            <div class="lt-notif-item lt-notif-item--unread" role="button" tabindex="0">
-              <span class="lt-notif-dot"></span>
+            <div class="lt-notif-item lt-notif-item--unread" role="button" tabindex="0" aria-label="Unread: Export CSV complete — 42 rows, 1 hr ago. Press Enter to dismiss.">
+              <span class="lt-notif-dot" aria-hidden="true"></span>
               <div class="lt-notif-item-body">
                 <div class="lt-notif-item-title">Export CSV complete — 42 rows</div>
                 <div class="lt-notif-item-time">1 hr ago</div>
               </div>
             </div>
-            <div class="lt-notif-item" role="button" tabindex="0">
-              <span class="lt-notif-dot lt-notif-dot--read"></span>
+            <div class="lt-notif-item" role="button" tabindex="0" aria-label="Scheduled maintenance completed, 3 hr ago. Press Enter to dismiss.">
+              <span class="lt-notif-dot lt-notif-dot--read" aria-hidden="true"></span>
               <div class="lt-notif-item-body">
                 <div class="lt-notif-item-title">Scheduled maintenance completed</div>
                 <div class="lt-notif-item-time">3 hr ago</div>
@@ -1098,7 +1098,7 @@
         <div class="lt-section-header">File Dropzone</div>
         <div class="lt-section-body">
           <div class="lt-dropzone" data-dropzone data-accept=".json,.csv,.log" data-max-size="10485760">
-            <input type="file" accept=".json,.csv,.log" multiple>
+            <input type="file" accept=".json,.csv,.log" multiple aria-label="Upload JSON, CSV, or log files (max 10 MB each)">
             <div class="lt-dropzone-icon">⤓</div>
             <div class="lt-dropzone-text">Drop files here or <strong>click to browse</strong></div>
             <div class="lt-dropzone-hint">Accepts .json, .csv, .log — max 10 MB each</div>
@@ -1284,7 +1284,7 @@
       <div class="lt-section-body">
         <div class="lt-grid lt-grid-2" style="gap:1.5rem">
           <div>
-            <label class="lt-label">Assign Workers (multi-select)</label>
+            <label class="lt-label" for="demo-combobox-input">Assign Workers (multi-select)</label>
             <div class="lt-combobox" id="demo-combobox">
               <div class="lt-combobox-input-wrap">
                 <input type="text" class="lt-combobox-input" id="demo-combobox-input" placeholder="Search workers…" autocomplete="off">
@@ -1293,7 +1293,7 @@
             </div>
           </div>
           <div>
-            <label class="lt-label">Search Tickets (typeahead)</label>
+            <label class="lt-label" for="demo-typeahead-input">Search Tickets (typeahead)</label>
             <div class="lt-typeahead" id="demo-typeahead">
               <input type="text" class="lt-input lt-w-full" id="demo-typeahead-input" placeholder="Type to search…" autocomplete="off">
               <div class="lt-typeahead-dropdown"></div>
@@ -1750,7 +1750,7 @@ Storage array link-down on `compute-storage-01`.
         const label = wrap && wrap.querySelector('.lt-range-value');
         if (label) {
           label.textContent = r.value;
-          r.addEventListener('input', () => { label.textContent = r.value; });
+          r.addEventListener('input', () => { label.textContent = r.value; r.setAttribute('aria-valuenow', r.value); });
         }
       });
 

base.js

@@ -1616,7 +1616,7 @@
     const ov   = document.getElementById(ovId);
     if (_mnOpen) _mnSetOpen(false);
     drawer.classList.add('is-open');
-    drawer.setAttribute('aria-hidden', 'false');
+    drawer.removeAttribute('aria-hidden');
     if (ov) ov.classList.add('is-open');
     _lockScroll();
     if (triggerEl) _modalTriggers.set(drawer, triggerEl);
@@ -2175,12 +2175,19 @@
       if (!label) return;
       label.setAttribute('tabindex', '0');
       label.setAttribute('role', 'button');
-      const _toggle = () => group.classList.toggle('is-open');
+      const chevron = label.querySelector('.chevron, .lt-sidebar-chevron');
+      if (chevron) chevron.setAttribute('aria-hidden', 'true');
+      const _toggle = () => {
+        group.classList.toggle('is-open');
+        label.setAttribute('aria-expanded', group.classList.contains('is-open') ? 'true' : 'false');
+      };
+      label.setAttribute('aria-expanded', group.classList.contains('is-open') ? 'true' : 'false');
       label.addEventListener('click', _toggle);
       label.addEventListener('keydown', e => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); _toggle(); } });
       // Open group if it contains the active link
       if (group.querySelector('.lt-sidebar-sub-link.active, .lt-sidebar-sub-link[aria-current="page"]')) {
         group.classList.add('is-open');
+        label.setAttribute('aria-expanded', 'true');
       }
     });
   }
@@ -2581,6 +2588,7 @@
           if (!_overlay) return;
           _overlay.classList.remove('is-open');
           _unlockScroll();
+          if (_lbKeyBound) { document.removeEventListener('keydown', _lbKeyBound); _lbKeyBound = null; }
           if (_lbTrigger && document.contains(_lbTrigger)) { _lbTrigger.focus(); }
           _lbTrigger = null;
         },
@@ -2713,10 +2721,16 @@
         .replace(/\*(.+?)\*/g,         '<em>$1</em>')
         .replace(/__(.+?)__/g,         '<strong>$1</strong>')
         .replace(/_(.+?)_/g,           '<em>$1</em>')
-        // Links
-        .replace(/\[([^\]]+)\]\(([^)]+)\)/g, '<a href="$2" target="_blank" rel="noopener noreferrer">$1</a>')
-        // Images
-        .replace(/!\[([^\]]*)\]\(([^)]+)\)/g, '<img src="$2" alt="$1" style="max-width:100%">')
+        // Links — block javascript: and data: URIs
+        .replace(/\[([^\]]+)\]\(([^)]+)\)/g, (_, text, url) => {
+          const safeUrl = /^(https?:\/\/|\/|#|\.\.?\/)/i.test(url) ? url : '#';
+          return `<a href="${safeUrl}" target="_blank" rel="noopener noreferrer">${text}</a>`;
+        })
+        // Images — block javascript: and data: URIs
+        .replace(/!\[([^\]]*)\]\(([^)]+)\)/g, (_, alt, src) => {
+          const safeSrc = /^(https?:\/\/|\/|\.\.?\/)/i.test(src) ? src : '';
+          return `<img src="${safeSrc}" alt="${alt}" style="max-width:100%">`;
+        })
         // Blockquote
         .replace(/^&gt;\s(.+)$/gm, '<blockquote>$1</blockquote>')
         // Horizontal rule