fix(offline): replace blocking overlay with slim banner; add server settings link (#170)

When offline with no cached content, the full-screen OfflineOverlay blocked
all navigation including Settings, making it impossible to fix a broken
server config. Replace it with the same slim banner used in offline-cache mode.

- OfflineBanner now handles both cases: cache (existing) and no-cache (new)
- No-cache banner shows server name and a direct link to Settings → Server tab
- OfflineOverlay component is no longer used (import removed from App.tsx)
- All 8 locales: added offlineNoCacheBanner and serverSettings keys

Fixes #170

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/de.ts

@@ -337,6 +337,7 @@ export const deTranslation = {
     offlineTitle: 'Keine Serververbindung',
     offlineSubtitle: '{{server}} ist nicht erreichbar. Prüfe Netzwerk oder Server.',
     offlineModeBanner: 'Offline-Modus — Wiedergabe aus lokalem Cache',
+    offlineNoCacheBanner: 'Keine Serververbindung — {{server}} nicht erreichbar',
     offlineLibraryTitle: 'Offline-Bibliothek',
     offlineLibraryEmpty: 'Noch keine Alben gecacht. Online gehen, Album öffnen und "Offline verfügbar machen" klicken.',
     offlineAlbumCount: '{{n}} Album',
@@ -346,6 +347,7 @@ export const deTranslation = {
     offlineFilterPlaylists: 'Playlists',
     offlineFilterArtists: 'Diskografien',
     retry: 'Erneut versuchen',
+    serverSettings: 'Server-Einstellungen',
     lastfmConnected: 'Last.fm verbunden als @{{user}}',
     lastfmSessionInvalid: 'Session ungültig — klicken zum Neu-Verbinden',
   },