Add unit tests for SBOM ingestion and transformation

- Implement `SbomIngestServiceCollectionExtensionsTests` to verify the SBOM ingestion pipeline exports snapshots correctly.
- Create `SbomIngestTransformerTests` to ensure the transformation produces expected nodes and edges, including deduplication of license nodes and normalization of timestamps.
- Add `SbomSnapshotExporterTests` to test the export functionality for manifest, adjacency, nodes, and edges.
- Introduce `VexOverlayTransformerTests` to validate the transformation of VEX nodes and edges.
- Set up project file for the test project with necessary dependencies and configurations.
- Include JSON fixture files for testing purposes.

src/Signer/StellaOps.Signer/TASKS.md

@@ -2,6 +2,6 @@
 
 | ID | Status | Owner(s) | Depends on | Description | Exit Criteria |
 |----|--------|----------|------------|-------------|---------------|
-
+| SIGN-REPLAY-186-003 | TODO | Signing Guild | REPLAY-CORE-185-001 | Extend DSSE signing to cover replay manifests/input/output bundles with multi-profile crypto; update `docs/modules/signer/architecture.md` referencing `docs/replay/DETERMINISTIC_REPLAY.md` Section 5 and coordinate with Authority. | Replay signing integration tests pass; docs merged; Authority contract signed off. |
 
 > Update status columns (TODO / DOING / DONE / BLOCKED) in tandem with code changes and associated tests.