feat: Implement Filesystem and MongoDB provenance writers for PackRun execution context

- Added `FilesystemPackRunProvenanceWriter` to write provenance manifests to the filesystem.
- Introduced `MongoPackRunArtifactReader` to read artifacts from MongoDB.
- Created `MongoPackRunProvenanceWriter` to store provenance manifests in MongoDB.
- Developed unit tests for filesystem and MongoDB provenance writers.
- Established `ITimelineEventStore` and `ITimelineIngestionService` interfaces for timeline event handling.
- Implemented `TimelineIngestionService` to validate and persist timeline events with hashing.
- Created PostgreSQL schema and migration scripts for timeline indexing.
- Added dependency injection support for timeline indexer services.
- Developed tests for timeline ingestion and schema validation.

bench/reachability-benchmark/benchmark/truth/py-fastapi-guarded.json

@@ -0,0 +1,36 @@
+{
+  "version": "1.0.0",
+  "cases": [
+    {
+      "case_id": "py-fastapi-guarded:104",
+      "case_version": "1.0.0",
+      "notes": "Eval unreachable unless ALLOW_EXEC=true",
+      "sinks": [
+        {
+          "sink_id": "FastApiGuarded::handle_request",
+          "label": "unreachable",
+          "confidence": "high",
+          "dynamic_evidence": {
+            "covered_by_tests": [
+              "tests/test_unreachable.py"
+            ],
+            "coverage_files": [
+              "outputs/coverage.json"
+            ]
+          },
+          "static_evidence": {
+            "call_path": [
+              "POST /exec",
+              "app.handle_request",
+              "guard: ALLOW_EXEC!=true"
+            ]
+          },
+          "config_conditions": [
+            "ALLOW_EXEC == 'true'"
+          ],
+          "notes": "Feature flag blocks sink by default"
+        }
+      ]
+    }
+  ]
+}