Accessibility pass: ARIA roles, label associations, CSS class migrations

- Add role=dialog/aria-modal/aria-labelledby to all 12 modal overlays (JS + PHP)
- Add aria-label="Close" to all 14 modal close buttons
- Add full ARIA combobox pattern to @mention autocomplete (listbox, option, aria-selected, aria-expanded)
- Add for= attributes to admin filter form labels (AuditLog, UserActivity, ApiKeys)
- Remove dead closeOnAdvancedSearchBackdropClick() from advanced-search.js

CSS/JS style cleanup:
- Move .ascii-banner static styles from JS inline to CSS class; add .ascii-banner--glow
- Add .ascii-banner-cursor, .loading-overlay--hiding, .has-overlay, tr[data-clickable]
- Add .animate-fadein/.animate-fadeout/.comment--deleting to ticket.css
- Add .lt-toast--hiding to base.css; remove opacity/transition inline JS
- Remove redundant cursor:pointer JS (already in th{} CSS rule)
- Remove trailing space in lt-select class attributes

Bug fixes:
- base.js: boot overlay opacity inline style was overriding .fade-out class opacity via
  specificity (1000 vs 20), preventing the fade-out animation — removed
- ascii-banner.js: cursor used blink-caret (border-color only) instead of blink-cursor
  (opacity-based), so the █ cursor never actually blinked — fixed

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

assets/js/ascii-banner.js

@@ -65,20 +65,8 @@ function renderASCIIBanner(bannerId, containerSelector, speed = 5, addGlow = tru
 
     // Create pre element for ASCII art
     const pre = document.createElement('pre');
-    pre.className = 'ascii-banner';
-    pre.style.margin = '0';
-    pre.style.fontFamily = 'var(--font-mono)';
-    pre.style.color = 'var(--terminal-green)';
-
-    if (addGlow) {
-        pre.style.textShadow = 'var(--glow-green)';
-    }
-
+    pre.className = addGlow ? 'ascii-banner ascii-banner--glow' : 'ascii-banner';
     pre.style.fontSize = getBannerFontSize(bannerId);
-    pre.style.lineHeight = '1.2';
-    pre.style.whiteSpace = 'pre';
-    pre.style.overflow = 'visible';
-    pre.style.textAlign = 'center';
 
     container.appendChild(pre);
 
@@ -178,8 +166,7 @@ function animatedWelcome(containerSelector) {
         banner.addEventListener('bannerComplete', () => {
             const cursor = document.createElement('span');
             cursor.textContent = '█';
-            cursor.style.animation = 'blink-caret 0.75s step-end infinite';
-            cursor.style.marginLeft = '5px';
+            cursor.className = 'ascii-banner-cursor';
             banner.appendChild(cursor);
         });
     }