Add unit and integration tests for VexCandidateEmitter and SmartDiff repositories

- Implemented comprehensive unit tests for VexCandidateEmitter to validate candidate emission logic based on various scenarios including absent and present APIs, confidence thresholds, and rate limiting.
- Added integration tests for SmartDiff PostgreSQL repositories, covering snapshot storage and retrieval, candidate storage, and material risk change handling.
- Ensured tests validate correct behavior for storing, retrieving, and querying snapshots and candidates, including edge cases and expected outcomes.

docs/airgap/bundle-repositories.md

@@ -2,7 +2,7 @@
 
 ## Scope
 - Deterministic storage for offline bundle metadata with tenant isolation (RLS) and stable ordering.
-- Ready for Mongo-backed implementation while providing in-memory deterministic reference behavior.
+- Ready for PostgreSQL-backed implementation while providing in-memory deterministic reference behavior.
 
 ## Schema (logical)
 - `bundle_catalog`:
@@ -25,13 +25,13 @@
 - Models: `BundleCatalogEntry`, `BundleItem`.
 - Tests cover upsert overwrite semantics, tenant isolation, and deterministic ordering (`tests/AirGap/StellaOps.AirGap.Importer.Tests/InMemoryBundleRepositoriesTests.cs`).
 
-## Migration notes (for Mongo/SQL backends)
+## Migration notes (for PostgreSQL backends)
 - Create compound unique indexes on (`tenant_id`, `bundle_id`) for catalog; (`tenant_id`, `bundle_id`, `path`) for items.
 - Enforce RLS by always scoping queries to `tenant_id` and validating it at repository boundary (as done in in-memory reference impl).
 - Keep paths lowercased or use ordinal comparisons to avoid locale drift; sort before persistence to preserve determinism.
 
 ## Next steps
-- Implement Mongo-backed repositories mirroring the deterministic behavior and indexes above.
+- Implement PostgreSQL-backed repositories mirroring the deterministic behavior and indexes above.
 - Wire repositories into importer service/CLI once storage provider is selected.
 
 ## Owners