feat(GRO-1427): add buffer rules CRUD — enums, table, routes

Re-implement lost commit from worktree cleanup. PR #12 already has
UAT_PLAYBOOK + factories fix; add all missing core implementation:
- Add petSizeCategoryEnum/coatTypeEnum to schema
- Add bufferRules table with service FK + unique constraint
- Add defaultBufferMinutes column to services table
- Change pets.coatType/petSizeCategory text columns to use enums
- Add routes/buffer-rules.ts: GET/POST/PATCH/DELETE, manager role guard
- Register /api/buffer-rules in index.ts
- Update services.ts PATCH to accept defaultBufferMinutes
- Update pets.ts POST/PATCH to accept sizeCategory/coatType
- Cast coatType/petSizeCategory in book.ts insert to match new enums
- Add 0031_buffer_rules.sql migration
- Fix factories.ts buildService to include defaultBufferMinutes: null

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packages/db/src/factories.ts

@@ -121,6 +121,7 @@ export function buildService(overrides: Partial<ServiceRow> = {}): ServiceRow {
     description: "A grooming service",
     basePriceCents: 6500,
     durationMinutes: 60,
+    defaultBufferMinutes: null,
     active: true,
     createdAt: new Date("2025-01-01T00:00:00Z"),
     updatedAt: new Date("2025-01-01T00:00:00Z"),