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.

tests/acceptance/packs/guardrails/README.md

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+# Acceptance Tests Guardrail Pack (Placeholder)
+
+Placeholder for the signed acceptance pack covering AT1–AT10.
+
+- Deterministic fixtures with fixed seeds and UTC timestamps.
+- DSSE envelopes for pack manifests; offline verification only.
+- Version pins live in `inputs.lock`.
+- Map to AT1–AT10:
+  - AT1 admission controls
+  - AT2 VEX handling
+  - AT3 authz flow
+  - AT4 replay parity
+  - AT5 policy DSSE negative tests
+  - AT6 PITR rehearsal
+  - AT7 offline guardrail pack
+  - AT8 gating thresholds
+  - AT9 reporting SLOs
+  - AT10 schema/signing coverage