Phase 11: Add structured logging and metrics coverage

[rpmoore]

Roadmap step 90 from docs/steps.md.

Scope

Add structured logging and metrics coverage.

Details

Distinguish cache latency, upstream latency, policy blocks, parse errors, DB failures, ingestion failures, admin mutations, and dropped query logs.

References

• docs/steps.md Phase 11, step 90
• docs/plan/07-operations-testing.md#logging
• docs/plan/07-operations-testing.md#metrics
• docs/plan/09-reviewer-concerns.md#concern-response-matrix