Implement ledger metrics for observability and add tests for Ruby packages endpoints

- Added `LedgerMetrics` class to record write latency and total events for ledger operations.
- Created comprehensive tests for Ruby packages endpoints, covering scenarios for missing inventory, successful retrieval, and identifier handling.
- Introduced `TestSurfaceSecretsScope` for managing environment variables during tests.
- Developed `ProvenanceMongoExtensions` for attaching DSSE provenance and trust information to event documents.
- Implemented `EventProvenanceWriter` and `EventWriter` classes for managing event provenance in MongoDB.
- Established MongoDB indexes for efficient querying of events based on provenance and trust.
- Added models and JSON parsing logic for DSSE provenance and trust information.

docs/modules/policy/TASKS.md

@@ -3,3 +3,4 @@
 | Task ID | State | Notes |
 | --- | --- | --- |
 | `SCANNER-POLICY-0001` | DONE (2025-11-10) | Ruby component predicates implemented in engine/tests, DSL docs updated, offline kit verifies `seed-data/analyzers/ruby/git-sources`. |
+| `DOCS-AIAI-31-006` | DONE (2025-11-13) | Published `docs/policy/assistant-parameters.md` capturing Advisory AI configuration knobs (inference/guardrails/cache/queue) and linked it from the module architecture dossier. |