Implement file storage layer with local provider, upload/download API, tests

- StorageProvider interface with LocalProvider (S3 placeholder)
- File table with entity_type/entity_id references, content type, path
- POST /v1/files (multipart upload), GET /v1/files (list by entity),
  GET /v1/files/:id (metadata), GET /v1/files/serve/* (content),
  DELETE /v1/files/:id
- member_identifier drops base64 columns, uses file_id FKs
- File validation: type whitelist, size limits, per-entity max
- Fastify storage plugin injects provider into app
- 6 API tests for upload, list, get, delete, validation
- Test runner kills stale port before starting backend

packages/shared/src/schemas/account.schema.ts

@@ -66,8 +66,8 @@ export const MemberIdentifierCreateSchema = z.object({
   issuingAuthority: opt(z.string().max(255)),
   issuedDate: opt(z.string().date()),
   expiresAt: opt(z.string().date()),
-  imageFront: opt(z.string()),
-  imageBack: opt(z.string()),
+  imageFrontFileId: opt(z.string().uuid()),
+  imageBackFileId: opt(z.string().uuid()),
   notes: opt(z.string()),
   isPrimary: z.boolean().default(false),
 })