feat(admin): implement activity logs frontend page (Phase 6-7)

Complete implementation of admin activity logs dashboard with real-time
streaming capabilities. Admin users can now monitor all system activity
through a comprehensive web interface.

Features:
- Stats dashboard with 4 key metrics (total logs, unique users, failures, 24h activity)
- Category breakdown visualization with color-coded badges
- Advanced filtering (date range, category, action type, username, success/failure)
- Paginated log table (50 entries per page) with sort by timestamp
- Real-time streaming toggle using Socket.IO
- Color-coded action badges (blue=auth, green=event, purple=match, red=admin, yellow=chat)
- Admin-only access with automatic redirect for non-admin users
- Responsive design for mobile and desktop

Frontend Changes:
- Created ActivityLogsPage.jsx (600+ lines) with complete UI implementation
- Added 3 admin API methods to api.js (getActivityLogs, getActivityLogActions, getActivityLogStats)
- Added /admin/activity-logs route to App.jsx
- Added admin navigation link to Navbar (desktop & mobile) with Shield icon
- Only visible to users with isAdmin flag

Implementation Details:
- Uses getSocket() from socket service for real-time updates
- Joins 'admin_activity_logs' Socket.IO room on streaming enable
- Receives 'activity_log_entry' events and prepends to table (first page only)
- Comprehensive error handling and loading states
- Empty states for no data
- Clean disconnect handling when streaming disabled

Testing:
- Build successful (no errors)
- Ready for manual testing and verification

Phase 8 (Testing) remains for manual verification of all features.

frontend/src/App.jsx

@@ -18,6 +18,7 @@ import RatePartnerPage from './pages/RatePartnerPage';
 import HistoryPage from './pages/HistoryPage';
 import ProfilePage from './pages/ProfilePage';
 import PublicProfilePage from './pages/PublicProfilePage';
+import ActivityLogsPage from './pages/admin/ActivityLogsPage';
 import VerificationBanner from './components/common/VerificationBanner';
 import InstallPWA from './components/pwa/InstallPWA';
 
@@ -199,6 +200,16 @@ function App() {
             }
           />
 
+          {/* Admin Routes */}
+          <Route
+            path="/admin/activity-logs"
+            element={
+              <ProtectedRoute>
+                <ActivityLogsPage />
+              </ProtectedRoute>
+            }
+          />
+
           {/* Public Profile - must be before home route */}
           <Route
             path="/:username"