Add standalone API test runner with accounts and members suites

Custom test framework that starts the backend, creates a test DB, runs
migrations, and hits real HTTP endpoints. Supports --suite and --tag
filtering. 24 tests covering account CRUD, member inheritance, state
normalization, move, search, and auto-generated numbers. Run with
bun run api-test.

packages/backend/package.json

@@ -8,6 +8,7 @@
     "start": "bun run src/main.ts",
     "test": "bun test",
     "test:watch": "bun test --watch",
+    "api-test": "bun run api-tests/run.ts",
     "lint": "eslint src/",
     "db:generate": "bunx drizzle-kit generate",
     "db:migrate": "bunx drizzle-kit migrate",