feat(FN-3047): add cancellable auth flow with recoverable pending login UX

This merge implements a recoverable pending-login auth flow (FN-3047) across three phases: cancellable in-progress auth routes in the API, an extended auth client contract, and updated ModelOnboardingModal/SettingsModal UI with proper cancel-button visibility during logout. It also adds `dashboard-r

Fusion-Task-Id: FN-3047

packages/dashboard/app/components/SettingsModal.css

@@ -1238,6 +1238,11 @@
   color: var(--color-error);
   padding-right: 4px;
 }
+.auth-provider-actions-row {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--space-sm);
+}
 
 /* === Key Hint === */
 .auth-key-hint {
@@ -1560,6 +1565,11 @@
     margin-left: auto;
   }
 
+  .auth-provider-actions-row {
+    width: 100%;
+    justify-content: flex-end;
+  }
+
   .auth-provider-info {
     width: 100%;
     flex-basis: 100%;