feat(contact): add contact form with admin panel and navbar dropdown

Database changes:
- Added ContactMessage model to Prisma schema
- Fields: userId, username, firstName, lastName, email, subject, message, status, ipAddress
- Status enum: new, read, resolved
- Relation to User model

Backend changes:
- Added POST /api/public/contact endpoint for form submissions
- Works for both authenticated and non-authenticated users
- Validation for email, subject (3-255 chars), message (10-5000 chars)
- Activity logging for submissions
- Added admin endpoints:
  - GET /api/admin/contact-messages - list with filtering by status
  - GET /api/admin/contact-messages/:id - view single message (auto-marks as read)
  - PATCH /api/admin/contact-messages/:id/status - update status
  - DELETE /api/admin/contact-messages/:id - delete message

Frontend changes:
- Created ContactPage at /contact route
- For non-logged-in users: firstName, lastName, email, subject, message fields
- For logged-in users: auto-fills username, shows only email, subject, message
- Character counter for message (max 5000)
- Success screen with auto-redirect to homepage
- Created ContactMessagesPage at /admin/contact-messages
- Two-column layout: message list + detail view
- Filter by status (all, new, read, resolved)
- View message details with sender info and IP address
- Update status and delete messages
- Added admin dropdown menu to Navbar
  - Desktop: dropdown with Activity Logs and Contact Messages
  - Mobile: expandable submenu
  - Click outside to close on desktop
  - ChevronDown icon rotates when open

Note: CAPTCHA integration planned for future enhancement

frontend/src/services/api.js

@@ -505,6 +505,15 @@ export const publicAPI = {
     });
     return data;
   },
+
+  async submitContact(contactData) {
+    const data = await fetchAPI('/public/contact', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(contactData),
+    });
+    return data;
+  },
 };
 
 export { ApiError };