Add integration tests for Proof Chain and Reachability workflows

- Implement ProofChainTestFixture for PostgreSQL-backed integration tests.
- Create StellaOps.Integration.ProofChain project with necessary dependencies.
- Add ReachabilityIntegrationTests to validate call graph extraction and reachability analysis.
- Introduce ReachabilityTestFixture for managing corpus and fixture paths.
- Establish StellaOps.Integration.Reachability project with required references.
- Develop UnknownsWorkflowTests to cover the unknowns lifecycle: detection, ranking, escalation, and resolution.
- Create StellaOps.Integration.Unknowns project with dependencies for unknowns workflow.

.github/flaky-tests-quarantine.json

@@ -0,0 +1,12 @@
+{
+  "$schema": "https://stellaops.io/schemas/flaky-tests-quarantine.v1.json",
+  "version": "1.0.0",
+  "updated_at": "2025-01-15T00:00:00Z",
+  "policy": {
+    "consecutive_failures_to_quarantine": 2,
+    "quarantine_duration_days": 14,
+    "auto_reactivate_after_fix": true
+  },
+  "quarantined_tests": [],
+  "notes": "Tests are quarantined after 2 consecutive failures. Review and fix within 14 days or escalate."
+}