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/backend/api-tests/lib/context.ts

@@ -3,6 +3,8 @@ import { type TestResult, printSuiteHeader, printTestResult } from './reporter.j
 
 export interface TestContext {
   api: ApiClient
+  token: string
+  baseUrl: string
   test: (name: string, optsOrFn: { tags?: string[] } | (() => Promise<void>), maybeFn?: () => Promise<void>) => void
   assert: {
     status: (res: ApiResponse, expected: number) => void
@@ -117,6 +119,8 @@ export async function runSuite(
 
   const ctx: TestContext = {
     api,
+    token,
+    baseUrl,
     assert: makeAssert(),
     test(name, optsOrFn, maybeFn) {
       const opts = typeof optsOrFn === 'function' ? {} : optsOrFn