Simplify tray: static template icon, click focuses the app

The setImage-swapped progress frames lost the template treatment on macOS and
rendered black-on-dark once transfers started. Dial back per user decision:
the tray is now just the glyph (template image set once at construction, never
swapped) and clicking it activates the window — no menu, no progress effects.
Removes everything that only served the fancy version: progress frames +
generation, engine.aggregateProgress, the workspacesSync webview->bun channel
(schema, send proxy, panels effect, handlers) and the activate-tab action.

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

ui/src/app/app.ts

@@ -67,13 +67,8 @@ export class App {
     });
   }
 
-  /** Native application-menu / tray actions forwarded from the bun process. */
+  /** Native application-menu 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);