fix(settings): protect unsaved edits on window close, quit, and reload

The settingsUnsavedChangesGuard only covers router navigation; closing
the Electron window, quitting the app, or reloading the page silently
dropped staged settings edits.

Renderer: SettingsUnloadGuardService (provided by SettingsComponent)
arms a beforeunload handler while the form is dirty — native leave
prompt in the PWA, cancelled-and-redialogued reload in Electron — and
mirrors the dirty state to the main process.

Main process: WindowCloseGuard intercepts BrowserWindow close before
beforeunload fires, pushes WINDOW:CLOSE_REQUESTED to the renderer for
the same save/discard/stay dialog, and replays the original intent
(close vs. quit, tracked via before-quit) only after the renderer
confirms. A failed save never confirms, keeping the guard's semantics.
The guard disarms on renderer navigation, crash, or destroyed
webContents so a window can never become unclosable.

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

libs/shared/interfaces/src/lib/electron-api.interface.ts

@@ -618,6 +618,18 @@ export interface ElectronBridgeApi {
     onWindowStateChange: (
         callback: (state: ElectronBridgeWindowState) => void
     ) => () => void;
+    /**
+     * While active, the main process intercepts window close / app quit and
+     * pushes a close request to the renderer instead of closing. Used by the
+     * settings page while its form holds unsaved edits.
+     */
+    setWindowCloseGuard: (active: boolean) => Promise<void>;
+    /**
+     * Completes a close the guard intercepted: the main process re-runs the
+     * original intent (window close or app quit) with the guard bypassed.
+     */
+    confirmWindowClose: () => Promise<void>;
+    onWindowCloseRequested: (callback: () => void) => () => void;
     fetchPlaylistByUrl: (
         url: string,
         title?: string,

libs/shared/interfaces/src/lib/ipc-commands.ts

@@ -113,3 +113,9 @@ export const WINDOW_TOGGLE_MAXIMIZE = 'WINDOW:TOGGLE_MAXIMIZE';
 export const WINDOW_CLOSE = 'WINDOW:CLOSE';
 export const WINDOW_GET_STATE = 'WINDOW:GET_STATE';
 export const WINDOW_STATE_CHANGED = 'WINDOW:STATE_CHANGED';
+
+// Close guard: while active, closing/quitting the app is intercepted in the
+// main process and handed to the renderer for a save/discard/stay decision
+export const WINDOW_SET_CLOSE_GUARD = 'WINDOW:SET_CLOSE_GUARD';
+export const WINDOW_CONFIRM_CLOSE = 'WINDOW:CONFIRM_CLOSE';
+export const WINDOW_CLOSE_REQUESTED = 'WINDOW:CLOSE_REQUESTED';