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>

src/routes/book.ts

@@ -193,8 +193,8 @@ bookRouter.post(
         name: body.petName,
         species: body.petSpecies,
         breed: body.petBreed ?? null,
-        coatType: body.petCoatType ?? null,
-        petSizeCategory: body.petSizeCategory ?? null,
+        coatType: (body.petCoatType ?? null) as "smooth" | "double" | "wire" | "curly" | "long" | "hairless" | null,
+        petSizeCategory: (body.petSizeCategory ?? null) as "small" | "medium" | "large" | "xlarge" | null,
       })
       .returning();
     const pet = petInserted[0];