Add comprehensive trace logging and observability features:
- Enhanced trace store with owner-scoped queries, filtering (agent, action,
time range), pagination, streaming export, and retention cleanup
- REST API endpoints: GET /api/traces (list with filters), GET /api/traces/export
(streaming JSON/CSV), GET /api/traces/stats (action counts)
- Owner isolation enforced at every layer (store, API, tests)
- Hand-rolled Prometheus metrics (pure Go, zero CGO): traces_total,
traces_by_action, errors_total, active_agents at GET /metrics
- Configurable slog JSON handler with --log-level flag
- Request ID middleware for cross-referencing logs and traces
- Batch trace writing (64 entries or 100ms flush interval)
- Background retention cleanup via --trace-retention flag
- SQL migration 002 adds owner_id column and composite indexes
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
