feat: v0.6.0 light mode, command palette, dialogs, toasts

- Light mode with the house ☀/◐ toggle and lt_theme preference; light
  terminal palette; Claude runs with dark-ansi so its colours follow the
  palette; tmux and the statusLine use ANSI colours.
- Command palette (⌕, Ctrl+Shift+P) with session, terminal, view, link and
  help commands.
- .lt-modal dialogs for new/rename/end and a keyboard shortcuts sheet.
- .lt-toast results for actions, uploads, copy and CI.
- ttyd dropped the reply of fast one-shot commands; replies now wait for the
  browser to hang up, and the client hangs up as soon as it has one.
- Sessions panel re-fetches after an action instead of reusing a stale poll.

Closes #31
Closes #32
Closes #33
Closes #34
Closes #35

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/index.template.html

@@ -3,11 +3,20 @@
 <head>
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover, interactive-widget=resizes-content">
-<meta name="color-scheme" content="dark">
+<meta name="color-scheme" content="dark light">
 <meta name="theme-color" content="#030508">
 <meta name="generator" content="devdesk">
 <title>DevDesk</title>
 <link rel="icon" id="favicon" href="__FAVICON__">
+<script>
+  // Theme before first paint (same key as web_template's lt.theme), no dark flash.
+  try {
+    var t = localStorage.getItem('lt_theme');
+    if (t !== 'light' && t !== 'dark') t = matchMedia('(prefers-color-scheme: light)').matches ? 'light' : 'dark';
+    document.documentElement.setAttribute('data-theme', t);
+    document.documentElement.style.colorScheme = t;
+  } catch (e) { /* storage blocked: stay dark */ }
+</script>
 <!--STYLES-->
 </head>
 <body class="dd-app">
@@ -31,6 +40,8 @@
     <span class="lt-ws-status dd-ws" id="ws-status" data-state="connecting" role="status">
       <span class="lt-dot"></span><span id="ws-label">connecting</span>
     </span>
+    <button type="button" class="lt-btn lt-btn-ghost lt-btn-sm dd-cmd-btn" id="cmd-toggle" title="Command palette (Ctrl+Shift+P)" aria-label="Open command palette">⌕<span class="dd-cmd-kbd">&nbsp;⌃⇧P</span></button>
+    <button type="button" class="lt-theme-btn" id="theme-toggle" aria-label="Switch to light mode" title="Switch to light mode">☀</button>
     <div class="dd-more">
       <button type="button" class="lt-btn lt-btn-ghost lt-btn-sm dd-more-toggle" id="more-toggle" aria-haspopup="menu" aria-expanded="false" title="Settings" aria-label="Settings">⋯</button>
       <div class="dd-menu dd-more-menu" id="more-menu" role="menu" hidden>
@@ -43,6 +54,7 @@
           </span>
         </div>
         <button type="button" class="dd-menu-item" id="notify-toggle" role="menuitem">Desktop notifications</button>
+        <button type="button" class="dd-menu-item" id="help-open" role="menuitem">Keyboard shortcuts</button>
         <button type="button" class="dd-menu-item" id="fullscreen-toggle" role="menuitem" title="In Chromium, fullscreen also captures Ctrl+W/Ctrl+T for the terminal">Fullscreen</button>
         <div class="dd-menu-foot" id="version">devdesk</div>
       </div>
@@ -128,6 +140,9 @@
     <span class="lt-footer-hint"><span class="lt-footer-key">⇧drag</span>select</span>
     <span class="lt-footer-sep">│</span>
     <span class="lt-footer-hint"><span class="lt-footer-key">drop / paste</span>attach files</span>
+    <span class="lt-footer-sep">│</span>
+    <span class="lt-footer-hint"><span class="lt-footer-key">^⇧P</span>commands</span>
+    <button type="button" class="dd-footer-help" id="footer-help">all keys</button>
   </div>
   <div class="dd-keybar" id="keybar" role="toolbar" aria-label="Terminal keys" hidden>
     <button type="button" data-keys="esc">Esc</button>