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/rpc.service.ts

@@ -86,4 +86,21 @@ export class RpcService {
         },
     });
   }
+
+  /** Fire-and-forget messages to the bun process (e.g. workspacesSync). */
+  get send() {
+    const rpc = this.rpc;
+    if (!rpc) throw new Error('RPC is only available inside the desktop app');
+    const ready = this.ready;
+    return new Proxy({} as (typeof rpc)['send'], {
+      get:
+        (_target, message: string) =>
+        (payload?: unknown) => {
+          void ready.then(() => {
+            const messages = rpc.send as unknown as Record<string, (p?: unknown) => void>;
+            messages[message](payload);
+          });
+        },
+    });
+  }
 }