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>

README.md

@@ -25,6 +25,10 @@ remote server over SSH/SFTP, so you can move files **local↔remote**,
   (MB/s or Mbps), persisted across restarts.
 - On macOS the tab bar is fused with the window titlebar; other platforms keep
   a standard titlebar.
+- **Menu-bar (tray) icon**: template icon that adapts to light/dark; during
+  transfers it fades and fills an aggregate progress bar (delivered/total bytes
+  of the whole queue). Its menu lists your tabs with live per-tab transfer
+  info — click one to jump to it — plus Show and Quit.
 - **Edit files** (F4 / toolbar / File menu): a built-in editor works on local
   and remote files directly; or pick an external app (Options → Editor →
   Custom → Choose…). External edits of remote files download to a temp folder,