Add backend request logging hook

[dangzitou]

Summary

Backend requests currently do not emit a lightweight per-request log containing the HTTP method and path, making endpoint activity harder to trace. This PR adds a global Fastify onRequest hook in the backend app that logs each incoming request through the existing pino-backed app logger, then adds test coverage to verify the hook runs for injected requests.

Changes

• Add a global Fastify onRequest hook in apps/backend/src/app.ts that logs the incoming request method and URL/path using app.log.info.
• Use the existing Fastify/pino logger so request logs remain consistent with current backend logging output.
• Add app-level test coverage in apps/backend/src/tests/app.test.ts that spies on app.log.info and asserts an injected request emits the expected method and path payload.

Validation

• pnpm run test is the detected test command; not executed yet and still pending in this environment.
• pnpm run lint is the detected lint command; not executed yet and still pending in this environment.

Risks

• The log field uses request.url, which may include query strings; this matches Fastify behavior but may be broader than a strict path-only value.
• Tests that spy on app.log.info may be sensitive to Fastify or pino logger binding behavior.
• If buildApp registers external database or cache plugins during tests, mocks may be needed to avoid requiring external services.

[Harxhit]

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