feat(macos): set traffic-light position via Tauri builder API and sync with zoom

Use Tauri's native `traffic_light_position()` builder method to position
macOS window controls instead of runtime objc2 calls. A global AtomicU32
tracks the current zoom level so newly created windows reflect the latest
zoom. The frontend syncs zoom changes to the backend via a new
`update_traffic_light_position` command.

- Add `traffic_light_position()` to `apply_platform_window_style` builder
- Add `CURRENT_ZOOM` atomic and `traffic_light_position()` helper
- Register `update_traffic_light_position` Tauri command
- Add `syncTrafficLightPosition` in appearance-provider to sync on zoom
  change, mount, and cross-tab storage events
- Consolidate `ensure_windows_undecorated` calls into `post_window_setup`
- Remove dead `on_window_resized` no-op and its Resized event listener

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/tauri.ts

@@ -442,6 +442,12 @@ export async function mcpRemoveServer(
   })
 }
 
+// Appearance / window chrome
+
+export async function updateTrafficLightPosition(zoom: number): Promise<void> {
+  return invoke("update_traffic_light_position", { zoom: zoom as number })
+}
+
 // Folder history commands
 
 export async function loadFolderHistory(): Promise<FolderHistoryEntry[]> {