Add comprehensive feature request admin functionality

- Update data model to include status, adminReply, and updatedAt fields
- Hide user emails from public API responses for privacy
- Add admin-only endpoints: list, reply, update status, delete
- Create admin-feature-requests.html with full management UI
- Add status badges and admin replies to public feature requests page
- Add Feature Requests link to all admin page sidebars

Admin capabilities:
- View all feature requests with author emails (admin only)
- Reply to feature requests with admin responses visible to public
- Update status: pending, planned, in-progress, completed, declined
- Delete feature requests
- Filter and sort by status, votes, date

chat/public/admin-external-testing.html

@@ -33,6 +33,7 @@
         <a class="ghost" href="/admin/resources">Resources</a>
         <a class="ghost" href="/admin/external-testing">External Testing</a>
         <a class="ghost" href="/admin/contact-messages">Contact Messages</a>
+        <a class="ghost" href="/admin/feature-requests">Feature Requests</a>
         <a class="ghost" href="/admin/login">Login</a>
       </div>
     </aside>