feat(ui): Online Inbox settings tab + auth-code/PKCE login

New Settings tab: enable toggle, config fields, sign-in/out + status.
OnlineLoginService runs the PKCE loopback flow (Duende.IdentityModel.OidcClient
7.1.0), opens the system browser, captures the callback, hands the refresh
token to the Worker. en/de localized. Fixes: loopback callback URL built from
host:port base (avoids doubled redirect path); PollIntervalSeconds threaded
through the state DTO so it loads instead of resetting to 60.

Visual layout + the live sign-in round-trip need manual verification.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ClaudeDo.App/Program.cs

@@ -123,6 +123,7 @@ sealed class Program
         sc.AddTransient<Func<WorktreesOverviewModalViewModel>>(sp => () => sp.GetRequiredService<WorktreesOverviewModalViewModel>());
         sc.AddSingleton<IPrimeScheduleApi, WorkerPrimeScheduleApi>();
         sc.AddSingleton<INotesApi, WorkerNotesApi>();
+        sc.AddSingleton<IOnlineLoginService, OnlineLoginService>();
         sc.AddTransient<PrimeClaudeTabViewModel>();
         sc.AddTransient<SettingsModalViewModel>();
         sc.AddTransient<MergeModalViewModel>();