Add request-scoped UUID logging middleware + unit tests

[mattmorgis]

Motivation

The previous issues (#6/#7) were closed in favor of a single, consolidated task.
We need production-grade logging with per-request correlation and automated
verification in one PR.

Goals

1. Generate a UUIDv4 per HTTP request and propagate it via:
   • X-Request-ID response header
   • a contextvars.ContextVar so any log line can include it
2. Emit a single access-log entry per request (method, path, status, latency)
3. Enrich every log record with the request ID using a logging.Filter
4. Provide full unit-test coverage for the above behaviour
5. Use only the Python stdlib + FastAPI (no new deps)

Implementation Plan

1. New module app/logging_config.py
   a. _request_id_ctx: ContextVar[str|None] = ContextVar("request_id", default=None)
   b. class RequestIdFilter(logging.Filter) sets record.request_id
   c. configure_logging() calls logging.basicConfig(...) with format:
   %(asctime)s [%(levelname)s] [%(request_id)s] %(name)s: %(message)s
   and attaches the filter to the root logger.
   d. add_request_id_middleware(app: FastAPI) -> None — middleware that:
   • creates uuid.uuid4().hex per request
   • stores in ctx-var, records start time
   • awaits call_next
   • logs access line via logging.getLogger("app.access")
   • resets ctx-var and sets X-Request-ID header

2. Modify app/main.py
   • Import and call configure_logging() before FastAPI(...)
   • Call add_request_id_middleware(app) right after app creation
   • Remove old logging.basicConfig() block

3. Unit tests tests/test_request_id_logging.py

   def test_request_id_header(client):
       r = client.get("/health")
       rid = r.headers.get("X-Request-ID")
       assert rid and len(rid) == 32 and int(rid, 16)
   
   def test_request_id_in_logs(client, caplog):
       caplog.set_level("INFO")
       r = client.get("/health")
       rid = r.headers["X-Request-ID"]
       assert any(getattr(rec, "request_id", None) == rid for rec in caplog.records)

   • Re-use existing client fixture from tests/test_main.py.

4. Docs (tiny)
   • Update README.md within the same PR: add a "Logging & Request IDs"
   subsection explaining header + log format.

Acceptance Criteria

• uvicorn app.main:app runs; logs show request IDs
• Every response has an X-Request-ID header
• pytest passes; new tests succeed; coverage ≥ current baseline
• No new runtime dependencies

Files touched / added

• app/logging_config.py (NEW)
• app/main.py (EDIT)
• tests/test_request_id_logging.py (NEW)
• README.md (EDIT)

Labels

enhancement, logging