feat: complete UI/UX overhaul - dashboard unification, calendar UX, mobile optimization

- Dashboard redesign as command center with filters, quick actions, inline approve/reject
- Reusable components: BookingRow, BookingFilters, ActionMenu, BookingPreviewModal, BookingEditModal
- Calendar: drag & drop reschedule, eventClick preview modal, grid/list toggle
- Mobile: segmented control bookings/calendar toggle, compact pills, responsive layout
- Collapsible filters with active count badge
- Smart menu positioning with Teleport
- Calendar/list bidirectional data sync
- Navigation: unified History page, removed AdminPending
- Google Calendar OAuth integration
- Dark mode contrast improvements, breadcrumb navigation
- useLocalStorage composable for state persistence

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/.env.example

@@ -18,7 +18,10 @@ SMTP_PASSWORD=
 SMTP_FROM_ADDRESS=noreply@space-booking.local
 SMTP_ENABLED=false
 
+# Frontend URL (used for OAuth callback redirects)
+FRONTEND_URL=http://localhost:5173
+
 # Google Calendar Integration
 GOOGLE_CLIENT_ID=your_google_client_id_here
 GOOGLE_CLIENT_SECRET=your_google_client_secret_here
-GOOGLE_REDIRECT_URI=https://your-domain.com/api/integrations/google/callback
+GOOGLE_REDIRECT_URI=http://localhost:8000/api/integrations/google/callback