fix(reader): close stuck reader window on book load failure, closes #3932 (#3980)

When a book's underlying file is missing, opening it in a dedicated
reader window showed an error toast then navigated that window to
/library, leaving a leftover library-in-reader-window the user had
to close manually. Route the recovery through a new
closeReaderWindowOrGoToLibrary() that closes the dedicated reader
window (after ensuring the main library window is visible) and only
falls back to /library navigation in the main window or on web.

Also fix a related macOS issue: the reader's CloseRequested handler
was running handleCloseBooks and calling currentWindow.destroy() on
the main window, which tore down the active book and bypassed the
Rust close-to-hide handler — making Cmd+W / traffic-light close
quit the app from the reader page (vs. correctly hiding from the
library page) and lose the active book even when the window did
hide. Skip both the cleanup and destroy on macOS for the main
window so the Rust handler hides it with the book intact, matching
the macOS minimize-to-dock convention.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/readest-app/src/app/reader/components/ReaderContent.tsx

@@ -20,7 +20,11 @@ import { isTauriAppPlatform } from '@/services/environment';
 import { uniqueId } from '@/utils/misc';
 import { throttle } from '@/utils/throttle';
 import { eventDispatcher } from '@/utils/event';
-import { ensureMainLibraryWindow, navigateToLibrary } from '@/utils/nav';
+import {
+  closeReaderWindowOrGoToLibrary,
+  ensureMainLibraryWindow,
+  navigateToLibrary,
+} from '@/utils/nav';
 import { clearDiscordPresence } from '@/utils/discord';
 import { BOOK_IDS_SEPARATOR } from '@/services/constants';
 import { BookDetailModal } from '@/components/metadata';
@@ -74,7 +78,10 @@ const ReaderContent: React.FC<{ ids?: string; settings: SystemSettings }> = ({ i
           setErrorLoading(true);
           eventDispatcher.dispatch('toast', {
             message: _('Unable to open book'),
-            callback: () => navigateBackToLibrary(),
+            callback: async () => {
+              const service = await envConfig.getAppService();
+              await closeReaderWindowOrGoToLibrary(service, router);
+            },
             timeout: 2000,
             type: 'error',
           });