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-tauri/src/lib.rs

@@ -136,7 +136,9 @@ mod tauri_app {
                             .title(&entry.name)
                             .inner_size(1260.0, 860.0)
                             .min_inner_size(900.0, 600.0);
-                        let _ = windows::apply_platform_window_style(builder).build();
+                        if let Ok(w) = windows::apply_platform_window_style(builder).build() {
+                            windows::post_window_setup(&w);
+                        }
                     }
                 }
 
@@ -334,6 +336,7 @@ mod tauri_app {
                 windows::open_stash_window,
                 windows::open_push_window,
                 windows::open_project_boot_window,
+                windows::update_traffic_light_position,
                 project_boot::detect_package_manager,
                 project_boot::create_shadcn_project,
                 system_settings::get_system_proxy_settings,