Phase 7: Final cleanup - Remove deprecated booking/appointment code

Deleted deprecated files:
- backend/routes/booking.py
- frontend/app/admin/appointments/, booking/, appointments/, sum/, audit/
- frontend/app/utils/appointment.ts
- frontend/e2e/booking.spec.ts, appointments.spec.ts

Updated references:
- exchange/page.tsx: Use /api/exchange/slots instead of /api/booking/slots
- useRequireAuth.ts: Redirect to /admin/trades and /exchange
- profile.tsx, invites.tsx: Update fallback redirect
- E2E tests: Update all /audit references to /admin/trades
- profile.test.tsx: Update admin redirect test

frontend/app/hooks/useRequireAuth.ts

@@ -48,10 +48,10 @@ export function useRequireAuth(options: UseRequireAuthOptions = {}): UseRequireA
       // Redirect to the most appropriate page based on permissions
       const redirect =
         fallbackRedirect ??
-        (hasPermission(Permission.VIEW_AUDIT)
-          ? "/audit"
-          : hasPermission(Permission.VIEW_COUNTER)
-            ? "/"
+        (hasPermission(Permission.VIEW_ALL_EXCHANGES)
+          ? "/admin/trades"
+          : hasPermission(Permission.CREATE_EXCHANGE)
+            ? "/exchange"
             : "/login");
       router.push(redirect);
     }