feat: multi-pet client group booking (closes #10) (#31)

* feat: multi-pet client group booking (closes groombook/groombook#10) (GRO-27)

- Add appointment_groups table: links multiple appointments from one client visit
- Add group_id FK on appointments (nullable, backward-compatible)
- Add GET/POST/PATCH/DELETE /api/appointment-groups endpoints
  - POST creates group record + one appointment per pet atomically (with conflict checks)
  - DELETE soft-cancels all appointments in the group
- Add GroupBooking.tsx page at /group-bookings with:
  - Dynamic pet-slot form (min 2 pets, each with their own groomer/service/end time)
  - Auto-calculates end time from service duration
  - Group card list showing all pets, groomers, and statuses side-by-side
  - Client filter and cancel-all action
- Wire into nav and routing in App.tsx
- Export AppointmentGroup type; add groupId field to Appointment type

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* fix: remove eslint-disable for uninstalled react-hooks plugin; remove unused clientMap (GRO-27)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

---------

Co-authored-by: Groom Book CTO <cto@groombook.app>
Co-authored-by: Paperclip <noreply@paperclip.ing>

apps/api/src/index.ts

@@ -10,6 +10,7 @@ import { staffRouter } from "./routes/staff.js";
 import { invoicesRouter } from "./routes/invoices.js";
 import { bookRouter } from "./routes/book.js";
 import { reportsRouter } from "./routes/reports.js";
+import { appointmentGroupsRouter } from "./routes/appointmentGroups.js";
 import { authMiddleware } from "./middleware/auth.js";
 import { startReminderScheduler } from "./services/reminders.js";
 
@@ -42,6 +43,7 @@ api.route("/appointments", appointmentsRouter);
 api.route("/staff", staffRouter);
 api.route("/invoices", invoicesRouter);
 api.route("/reports", reportsRouter);
+api.route("/appointment-groups", appointmentGroupsRouter);
 
 const port = Number(process.env.PORT ?? 3000);
 console.log(`API server listening on port ${port}`);