feat(gro-48): row-level data scoping for groomer role (RBAC Phase 2)

Filter query results at the route handler level when staff role is groomer:

- GET /api/appointments: WHERE staffId = groomer OR batherStaffId = groomer
- GET /api/appointments/🆔 403 if not assigned to groomer (as staff or bather)
- GET /api/clients: Clients with ≥1 appointment for this groomer (via exists subquery)
- GET /api/clients/🆔 403 if no appointment linkage
- GET /api/pets: Pets owned by groomer-linked clients (via exists subquery)
- GET /api/pets/:petId: 403 if no appointment linkage

Managers and receptionists: no change.

Added exists to @groombook/db exports (was missing from re-export).
Added groomerIsolation unit tests for role guard and filter logic.

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

packages/db/src/index.ts

@@ -3,7 +3,7 @@ import postgres from "postgres";
 import * as schema from "./schema.js";
 
 export * from "./schema.js";
-export { and, asc, desc, eq, gte, gt, ilike, lt, lte, ne, or, sql } from "drizzle-orm";
+export { and, asc, desc, eq, exists, gte, gt, ilike, lt, lte, ne, or, sql } from "drizzle-orm";
 
 let _db: ReturnType<typeof drizzle> | null = null;