fix(macos): persist zoom level to DB so traffic lights use correct position on launch

Previously the welcome window (or any startup window) always used the
default CURRENT_ZOOM of 100, ignoring the user's saved zoom preference
stored in frontend localStorage. Now update_traffic_light_position also
writes the zoom value to the app_metadata DB, and setup() reads it back
before creating any window.

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

src-tauri/src/lib.rs

@@ -83,6 +83,10 @@ mod tauri_app {
                     }
                 }
 
+                // Load saved zoom level for traffic-light positioning before
+                // any window is created.
+                tauri::async_runtime::block_on(windows::load_saved_zoom(&db.conn));
+
                 // Install bundled expert skills into the central store
                 // (`~/.codeg/skills/`). Runs in the background and does
                 // not block startup; failures are logged but non-fatal.