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.Vndr.Oracle/AGENTS.md

@@ -7,7 +7,7 @@ Oracle PSIRT connector for Critical Patch Updates (CPU) and Security Alerts; aut
 - Persist raw documents; maintain source_state across cycles; idempotent mapping.
 ## Participants
 - Source.Common (HTTP, validators).
-- Storage.Mongo (document, dto, advisory, alias, affected, reference, psirt_flags, source_state).
+- Storage.Postgres (document, dto, advisory, alias, affected, reference, psirt_flags, source_state).
 - Models (canonical; affected ranges for vendor products).
 - Core/WebService (jobs: source:oracle:fetch|parse|map).
 - Merge engine (later) to prefer PSIRT ranges over NVD for Oracle products.
@@ -23,7 +23,7 @@ Out: signing or patch artifact downloads.
 - Logs: cycle tags, advisory ids, extraction timings; redact nothing sensitive.
 ## Tests
 - Author and review coverage in `../StellaOps.Concelier.Connector.Vndr.Oracle.Tests`.
-- Shared fixtures (e.g., `MongoIntegrationFixture`, `ConnectorTestHarness`) live in `../StellaOps.Concelier.Testing`.
+- Shared fixtures (e.g., `PostgresIntegrationFixture`, `ConnectorTestHarness`) live in `../StellaOps.Concelier.Testing`.
 - Keep fixtures deterministic; match new cases to real-world advisories or regression scenarios.
 
 ## Required Reading