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/profile/page.test.tsx

@@ -242,18 +242,18 @@ describe("ProfilePage - Access Control", () => {
     });
   });
 
-  test("redirects admin to audit page", async () => {
+  test("redirects admin to admin trades page", async () => {
     mockUser = {
       id: 1,
       email: "admin@example.com",
       roles: ["admin"],
-      permissions: ["view_audit"],
+      permissions: ["view_all_exchanges"],
     };
 
     render(<ProfilePage />);
 
     await waitFor(() => {
-      expect(mockPush).toHaveBeenCalledWith("/audit");
+      expect(mockPush).toHaveBeenCalledWith("/admin/trades");
     });
   });