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.

src/Concelier/__Libraries/StellaOps.Concelier.Connector.Acsc/AGENTS.md

@@ -11,13 +11,13 @@ Bootstrap the ACSC (Australian Cyber Security Centre) advisories connector so th
 
 ## Participants
 - `Source.Common` for HTTP client creation, fetch service, and DTO persistence helpers.
-- `Storage.Mongo` for raw/document/DTO/advisory storage plus cursor management.
+- `Storage.Postgres` for raw/document/DTO/advisory storage plus cursor management.
 - `Concelier.Models` for canonical advisory structures and provenance utilities.
 - `Concelier.Testing` for integration harnesses and snapshot helpers.
 
 ## Interfaces & Contracts
 - Job kinds should follow the pattern `acsc:fetch`, `acsc:parse`, `acsc:map`.
-- Documents persisted to Mongo must include ETag/Last-Modified metadata when the source exposes it.
+- Documents persisted to PostgreSQL must include ETag/Last-Modified metadata when the source exposes it.
 - Canonical advisories must emit aliases (ACSC ID + CVE IDs) and references (official bulletin + vendor notices).
 
 ## In/Out of scope