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.Worker/Hub/WorkerHub.cs

@@ -74,7 +74,8 @@ public record OnlineInboxStateDto(
     string ClientId,
     string Scopes,
     string RedirectUri,
-    bool SignedIn);
+    bool SignedIn,
+    int PollIntervalSeconds);
 
 public record OnlineInboxConfigInput(
     bool Enabled,
@@ -725,7 +726,8 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
             _onlineInboxConfig.Zitadel.ClientId,
             _onlineInboxConfig.Zitadel.Scopes,
             _onlineInboxConfig.RedirectUri,
-            signedIn);
+            signedIn,
+            _onlineInboxConfig.PollIntervalSeconds);
     }
 
     public void SetOnlineInboxConfig(OnlineInboxConfigInput input)