fix(ag-ui): hide sidebar launcher hint when App mode is on

In App mode the Google Map is the full-bleed background and the chat
sidebar floats over it, so the placeholder "Use the launcher…" hint
(projected into chat-sidebar's default content slot) floated unreadably
over the map. Gate it on appMode !== 'on' so it only shows in plain
sidebar mode where the area behind the chat is genuinely empty.

Verified via DOM probe: /sidebar appMode off → hint present (1);
/sidebar?appmode=on with the map mounted → hint absent (0).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: blove

examples/ag-ui/angular/src/app/modes/sidebar-mode.component.ts

@@ -22,9 +22,13 @@ import { WelcomeSuggestionsComponent } from './welcome-suggestions.component';
       (selectedModelChange)="shell.onModelChange($event)"
     >
       <div class="sidebar-mode__background">
-        <p class="sidebar-mode__hint">
-          Use the launcher (right edge) to dismiss or re-open the chat panel.
-        </p>
+        <!-- In App mode the map is the background; this placeholder hint would
+             float unreadably over it, so only show it in plain sidebar mode. -->
+        @if (shell.appMode() !== 'on') {
+          <p class="sidebar-mode__hint">
+            Use the launcher (right edge) to dismiss or re-open the chat panel.
+          </p>
+        }
       </div>
       <welcome-suggestions chatWelcomeSuggestions (selected)="send($event)" />
     </chat-sidebar>