Tray icon with live transfer progress and tabs menu

- AppTray: template menu-bar icon (22pt, adapts to light/dark). While
  transfers run it swaps to pre-rendered frames — faded arrows + a fill bar
  showing aggregate doneBytes/totalBytes of the queue (nearest 5%, throttled
  500ms); back to the glyph when idle. No runtime image encoding.
- Menu: one entry per tab (checkmark on the active one) with live per-tab
  transfer count and percentage (jobs mapped via session ids), an overall
  progress row while transferring, Show <app>, Quit. Selecting a tab
  activates the window and switches to it.
- First use of webview->bun messages: PanelsService pushes workspacesSync
  (tab names, sessions, active id) via a new ready-gated send proxy; verified
  end-to-end in the running app.
- engine.aggregateProgress(): totals + per-session breakdown over non-terminal
  jobs (unit-verified idle/mid-transfer/idle).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/app/app.ts

@@ -67,8 +67,13 @@ export class App {
     });
   }
 
-  /** Native application-menu actions forwarded from the bun process. */
+  /** Native application-menu / tray actions forwarded from the bun process. */
   private handleMenuAction(action: string): void {
+    if (action.startsWith('activate-tab:')) {
+      const id = Number(action.slice('activate-tab:'.length));
+      if (Number.isFinite(id)) this.panels.setActiveWorkspace(id);
+      return;
+    }
     if (action.startsWith('connect:')) {
       const id = action.slice('connect:'.length);
       const connection = this.connections.connections().find((c) => c.id === id);