feat(backend): implement request context propagation with trace IDs

[menawar]

feat(backend): implement request context propagation with trace IDs

Description

closes #84.

This Pull Request introduces distributed tracing semantics to the AgenticPay backend service. Prior to this PR, there was no consistent mechanism to trace logs or context across the lifecycle of a single request, making cross-service and asynchronous log debugging difficult.

This PR resolves the issue by utilizing Node.js's built-in AsyncLocalStorage to automatically track and propagate Trace IDs throughout the lifecycle of an HTTP request without needing to manually pass the trace context into every function.

Key Changes

• Trace ID Generation: Automatically generates a completely randomized v4 UUID via crypto.randomUUID() for any request that doesn't supply a pre-existing trace ID.
• Trace Context Propagation: Implements an Express middleware combined with AsyncLocalStorage to bind the active trace ID to the context of the running HTTP request path.
• Console Log Injection: Overrides the global native Node variants of console.log, console.info, console.error, and console.warn to proactively lookup the concurrent trace ID and prepend it securely to all terminal outputs automatically (e.g., [TraceID: 153a7b-83ce...]).
• HTTP Response Integration: Appends the active trace ID to all outgoing response headers via X-Trace-Id allowing the frontend clients or sibling services to align their logging schemas accordingly.

How to Test

1. Pull down the issue-84 branch and run the backend service:

   cd backend
   npm install && npm run build
   OPENAI_API_KEY="dummy-key" npm run dev

2. In a separate terminal, curl the health endpoint using an arbitrary Trace ID:

   curl -i -H "x-trace-id: custom-trace-1234" http://localhost:3001/health

3. Observe the curl terminal outputs receiving the X-Trace-Id: custom-trace-1234 response header.
4. Observe the backend server terminal automatically logging the lifecycle injected with the custom trace ID.

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