[enhancement] E3-3: No request/correlation IDs — impossible to trace across components

[OneStepAt4time]

Finding

ID: OBS-7 | Severity: 🟠 MEDIUM

StructuredLogRecord has no requestId, traceId, or spanId. Correlating logs for a single API call across components is impossible.

Fix Required

1. Enable Fastify's requestIdHeader + genReqId to generate UUID-v4 per request
2. Add requestId to StructuredLogRecord
3. Thread requestId through session.ts and monitor.ts for log correlation

Files: src/server.ts, src/logger.ts

Acceptance Criteria

All log records for a single HTTP request share the same requestId.

Milestone

M-E3: Observability