Improve frontend navigation and mobile UX

- Add mobile bottom tab bar for media browsing (Home, Libraries, Favourites, Playlists, More)
- Split mobile drawer: media links first, admin links under a Management section
- Show contextual back button in mobile header for deep routes
- Add reusable PageBackButton and PageHeader components
- Add back navigation to playlist detail, library page, and missing media state
- Embed queue panels in TaskQueuePage to avoid duplicate page titles
- Expose theme toggle in user menu on small screens

Co-authored-by: truewhile <truewhile@users.noreply.github.com>

web/src/pages/LibraryPage.tsx

@@ -13,6 +13,7 @@ import {
   type SortOrder,
 } from '../utils/mediaSort'
 import { LibraryPageDialogs } from './LibraryPageDialogs'
+import { PageBackButton } from '../components/PageBackButton'
 import { LibraryPageHeader } from './LibraryPageHeader'
 import { LibraryMediaSections } from './LibraryMediaSections'
 import { LibrarySeriesDetailSection } from './LibrarySeriesDetailSection'
@@ -181,6 +182,12 @@ export function LibraryPage() {
 
   return (
     <div className="space-y-6">
+      {!selectedSeries && (
+        <div className="hidden lg:block">
+          <PageBackButton to="/libraries" label="全部媒体库" compact />
+        </div>
+      )}
+
       {!selectedSeries && (
         <LibraryPageHeader
           library={library}