Add request ID middleware and correlate logs with request context

[Jennylila]

Overview

This PR adds request ID middleware and AsyncLocalStorage-backed log correlation so concurrent request logs can be traced through the system. Every incoming request gets a UUID, returned via X-Request-ID, and all log lines within that request automatically include the matching requestId.

Related Issue

Closes #34

Changes

🔗 Request ID Middleware

• [ADD] src/middleware/requestId.js
• Generates a UUID for every incoming request using crypto.randomUUID().
• Attaches the ID to req.id and sets the X-Request-ID response header.
• Runs downstream handlers inside AsyncLocalStorage so child log calls inherit request context without passing req manually.

📝 Logger Correlation

• [MODIFY] src/logger.js
• Added a Winston format that reads requestId from AsyncLocalStorage on every log line.
• Logs outside an active request context use requestId: 'system' (background jobs, startup, shutdown).

🚀 App Wiring

• [MODIFY] src/index.js
• Registered requestIdMiddleware early in the Express middleware chain.
• Fixed module export so server is defined when the app is imported in tests.

🧪 Tests

• [ADD] test/requestId.test.js
• Verifies X-Request-ID is present on responses.
• Verifies req.id matches the response header.
• Verifies AsyncLocalStorage context propagation.
• Verifies log output includes the matching requestId for a given request.
• Verifies background tasks log with requestId: 'system'.
• Verifies /health returns X-Request-ID.

🔧 Configuration

• [MODIFY] package.json
• Fixed a missing comma that prevented npm install from parsing dependencies.

Verification Results

npm test -- test/requestId.test.js ✅ passed (6/6)

Acceptance Criteria	Status
X-Request-ID header on every response	✅
Request ID propagated to all log lines within that request	✅
Background tasks log with requestId: 'system'	✅
Test: log output includes matching requestId for a given request	✅
ALS used (not req passed manually through every function)	✅