feat: add PolicyPackSelectorComponent with tests and integration

- Implemented PolicyPackSelectorComponent for selecting policy packs.
- Added unit tests for component behavior, including API success and error handling.
- Introduced monaco-workers type declarations for editor workers.
- Created acceptance tests for guardrails with stubs for AT1–AT10.
- Established SCA Failure Catalogue Fixtures for regression testing.
- Developed plugin determinism harness with stubs for PL1–PL10.
- Added scripts for evidence upload and verification processes.

scripts/packs/__fixtures__/good/approvals-ledger.dsse

@@ -0,0 +1,13 @@
+{
+  "schemaVersion": "stellaops.pack.approval-ledger.v1",
+  "runId": "run-1",
+  "gateId": "security-review",
+  "planHash": "sha256:ca3d163bab055381827226140568f3bef7eaac187cebd76878e0b63e9e442356",
+  "decision": "approved",
+  "decidedAt": "2025-12-05T00:00:00Z",
+  "tenantId": "demo-tenant",
+  "approver": {
+    "id": "approver@example.com",
+    "summary": "LGTM"
+  }
+}