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/zh.ts

@@ -336,11 +336,13 @@ export const zhTranslation = {
     offlineTitle: '无服务器连接',
     offlineSubtitle: '无法连接到 {{server}}。请检查您的网络或服务器。',
     offlineModeBanner: '离线模式 — 正在从本地缓存播放',
+    offlineNoCacheBanner: '无服务器连接 — 无法访问 {{server}}',
     offlineLibraryTitle: '离线音乐库',
     offlineLibraryEmpty: '尚未缓存任何专辑。请联网，打开专辑并点击"设为离线可用"。',
     offlineAlbumCount_one: '{{n}} 张专辑',
     offlineAlbumCount_plural: '{{n}} 张专辑',
     retry: '重试',
+    serverSettings: '服务器设置',
     lastfmConnected: 'Last.fm 已连接为 @{{user}}',
     lastfmSessionInvalid: '会话无效 — 点击重新连接',
   },