Replace manual backend config with auto JWT auth

Device auto-registers on first launch using hardcoded backend URL
and anon key (MarksAuth.swift). 90-day JWT stored in UserDefaults,
refreshed transparently. No settings fields needed — ClaudeService
is always active and non-optional throughout the app.

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

Marks/MarksApp.swift

@@ -32,8 +32,7 @@ struct MainContainer: View {
         self.config = config
         self.onDisconnect = onDisconnect
         let api = LinkdingAPI(config: config)
-        let claude = ClaudeService.load()
-        _viewModel = State(wrappedValue: BookmarksViewModel(api: api, claude: claude, cacheKey: config.host))
+        _viewModel = State(wrappedValue: BookmarksViewModel(api: api, cacheKey: config.host))
     }
 
     var body: some View {