fix: address PR #102 review feedback (GRO-145)

- factories.ts: add photoKey/photoUploadedAt null defaults to buildPet (TS regression fix)
- s3.ts: lazy singleton S3Client to avoid re-instantiation per call
- routes/pets.ts: server-side 5MB file size limit, explicit content-type allowlist (drops image/svg+xml etc), validate confirm key ownership against pets/${petId}/ prefix, delete old S3 object on re-upload, fix RBAC comment on DELETE photo
- PetPhotoUpload.tsx: bypass canvas resize for GIFs (preserves animation), pass fileSizeBytes in upload-url request
- Add PetPhotoDisplay.test.tsx: 7 tests covering fetch states, placeholder, refetch on petId change, custom size
- Add PetPhotoUpload.test.tsx: 8 tests covering idle state, type validation, upload flow, progress, GIF bypass
- Update petPhotos.test.ts: add SVG rejection, 5MB limit, key ownership, and old-photo deletion tests (18 total)

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

packages/db/src/factories.ts

@@ -92,6 +92,8 @@ export function buildPet(overrides: Partial<PetRow> & { clientId: string }): Pet
     shampooPreference: null,
     specialCareNotes: null,
     customFields: {},
+    photoKey: null,
+    photoUploadedAt: null,
     createdAt: new Date("2025-01-01T00:00:00Z"),
     updatedAt: new Date("2025-01-01T00:00:00Z"),
   };