Add MongoDB storage library and update acceptance tests with deterministic stubs

- Created StellaOps.Notify.Storage.Mongo project with initial configuration.
- Added expected output files for acceptance tests (at1.txt to at10.txt).
- Added fixture input files for acceptance tests (at1 to at10).
- Created input and signature files for test cases fc1 to fc5.

docs/runbooks/vuln-ops.md

@@ -14,4 +14,9 @@
 - Export failures: bundle retry, manifest verification, hash checks.
 - Policy activation: rollout checklist and rollback.
 
+### Hash Capture Checklist (when scenarios scripted)
+- `assets/vuln-explorer/runbook-projector-lag.md`
+- `assets/vuln-explorer/runbook-resolver-storm.json`
+- `assets/vuln-explorer/runbook-export-failure.json`
+- `assets/vuln-explorer/runbook-policy-activation.md`
 _Last updated: 2025-12-05 (UTC)_