feat: rename History tab to Library and show local library items

- Rename bottom navigation 'History' to 'Library'
- Add Local Library section showing scanned tracks below downloaded tracks
- Add source badge to each item (Downloaded/Local) for clear identification
- Add new localization strings for Library tab and source badges
- Local library items can be played directly from the library tab

lib/screens/main_shell.dart

@@ -202,14 +202,14 @@ class _MainShellState extends ConsumerState<MainShell> {
         icon: Badge(
           isLabelVisible: queueState > 0,
           label: Text('$queueState'),
-          child: const Icon(Icons.history_outlined),
+          child: const Icon(Icons.library_music_outlined),
         ),
         selectedIcon: Badge(
           isLabelVisible: queueState > 0,
           label: Text('$queueState'),
-          child: const Icon(Icons.history),
+          child: const Icon(Icons.library_music),
         ),
-        label: l10n.navHistory,
+        label: l10n.navLibrary,
       ),
       if (showStore)
         NavigationDestination(