feat(desktop): macOS menu bar tray with live session state and mini-chat UX

Add an always-visible macOS status bar (tray) item that surfaces OpenChamber's
live state and acts as a quick launcher, plus a series of related desktop UX
fixes around mini-chat, window routing, notifications and shortcuts.

Tray (new):
- Monochrome template cube glyph that adapts to the menu bar light/dark.
- Icon-driven activity indicator: a smooth, eased, infinite "breathing" fill
  while sessions are busy; a static filled cube when finished sessions are left
  unread; a plain outline when idle. Text counters next to the icon only for
  actionable states (pending approvals, errors).
- Menu lists active sessions (status glyph, branch, unread count) with overflow
  rolled into a submenu; pending permission/question approvals with inline
  Allow once / Allow always / Deny; quick actions (New Session, New Mini Chat,
  Show OpenChamber, Quit). Header shows the active instance name
  ("Local OpenChamber" or the remote host label) for multi-window clarity.
- Session list sourced from the global (cross-project) sessions store, sorted by
  last-updated, independent of which directories are currently open; live
  status/unread/branch merged in from directory sync stores where available.
  Sub-session (multi-run) activity rolls up to the parent row.
- Event-driven updates (global store + directory stores + notifications +
  registry) with a short debounce; polling kept only as a slow safety net.

Tray/window routing:
- Opening a session from the tray targets the surface the user was last on: if a
  mini-chat is active it switches that existing window to the session in place
  (no new window); otherwise the main window (revealed without a reload).
- app.activate (dock click) restores the last-focused/minimized window instead
  of spawning a new main window; only creates one when nothing is left.
- "Open in main window" and tray session-open now create the main window when
  none exists, queuing the session as a pending deep-link so it opens once the
  fresh renderer is ready.

Mini chat:
- New Mini Chat is now a customizable shortcut, exposed in Settings > Shortcuts,
  in the File menu (hint only, renderer owns the binding), and in the tray.
- Themed splash backdrop on window open to remove the white flash / flicker;
  dismissed once content is ready, leaving the content's single cube logo.
- Mini-chat can switch sessions in place via openchamber:open-session.

Notifications:
- The active/selected session only counts as "seen" when the window is focused,
  so turns completing while the app is backgrounded raise an unread marker;
  refocusing the window clears it.

packages/web/mini-chat.html

@@ -4,9 +4,95 @@
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no, viewport-fit=cover" />
     <title>OpenChamber Mini Chat</title>
+
+    <script>
+      // Apply theme + splash colors before first paint so the window opens on a
+      // branded splash instead of flashing white while React/CSS load.
+      (function() {
+        try {
+          var themeMode = localStorage.getItem('themeMode');
+          var variant = localStorage.getItem('selectedThemeVariant');
+          var useSystem = localStorage.getItem('useSystemTheme');
+          var isDark;
+
+          if (themeMode === 'dark') {
+            isDark = true;
+          } else if (themeMode === 'light') {
+            isDark = false;
+          } else if (themeMode === 'system' || useSystem === null || useSystem === 'true') {
+            isDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
+          } else if (variant === 'light' || variant === 'dark') {
+            isDark = variant === 'dark';
+          } else {
+            isDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
+          }
+
+          document.documentElement.classList.add(isDark ? 'dark' : 'light');
+          document.documentElement.setAttribute('data-splash-variant', isDark ? 'dark' : 'light');
+          document.documentElement.style.setProperty('color-scheme', isDark ? 'dark' : 'light');
+
+          var splashBgLight = localStorage.getItem('splashBgLight');
+          var splashFgLight = localStorage.getItem('splashFgLight');
+          var splashBgDark = localStorage.getItem('splashBgDark');
+          var splashFgDark = localStorage.getItem('splashFgDark');
+
+          if (splashBgLight) document.documentElement.style.setProperty('--splash-background-light', splashBgLight);
+          if (splashFgLight) document.documentElement.style.setProperty('--splash-stroke-light', splashFgLight);
+          if (splashBgDark) document.documentElement.style.setProperty('--splash-background-dark', splashBgDark);
+          if (splashFgDark) document.documentElement.style.setProperty('--splash-stroke-dark', splashFgDark);
+        } catch (error) {
+          console.warn('Failed to apply theme:', error);
+        }
+      })();
+    </script>
+
+    <style>
+      /* A plain themed backdrop — no logo. The mini-chat content renders its
+         own (single) OpenChamber cube in its empty state, so a cube here would
+         briefly show a second, differently-sized one before handing off. The
+         backdrop matches bg-background, so fading it out is seamless. */
+      :root {
+        --splash-background-dark: #151313;
+        --splash-background-light: #FFFCF0;
+        --splash-background: var(--splash-background-dark);
+      }
+      html[data-splash-variant='light'] { --splash-background: var(--splash-background-light); }
+      html[data-splash-variant='dark'] { --splash-background: var(--splash-background-dark); }
+
+      #initial-loading {
+        background-color: var(--splash-background);
+        height: 100vh;
+        width: 100%;
+        position: absolute;
+        inset: 0;
+        z-index: 9999;
+        transition: opacity 0.3s ease-out;
+      }
+      #initial-loading.fade-out {
+        opacity: 0;
+        pointer-events: none;
+      }
+    </style>
+
     <script type="module" src="/src/mini-chat-main.tsx"></script>
   </head>
   <body class="h-full bg-background text-foreground">
-    <div id="root" class="h-full"></div>
+    <div id="root" class="h-full">
+      <!-- Themed backdrop until the mini-chat React app is ready (dismissed in
+           ElectronMiniChatApp). No logo here on purpose — the content renders
+           the single OpenChamber cube itself. -->
+      <div id="initial-loading"></div>
+    </div>
+
+    <script>
+      // Safety net: never let the splash hang if the app fails to dismiss it.
+      setTimeout(function() {
+        var loading = document.getElementById('initial-loading');
+        if (loading) {
+          loading.classList.add('fade-out');
+          setTimeout(function() { loading.remove(); }, 300);
+        }
+      }, 8000);
+    </script>
   </body>
 </html>