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.

src/TaskRunner/StellaOps.TaskRunner/StellaOps.TaskRunner.WebService/Program.cs

@@ -319,6 +319,11 @@ async Task<IResult> HandleApplyApprovalDecision(
         return Results.BadRequest(new { error = "planHash is required." });
     }
 
+    if (!Regex.IsMatch(request.PlanHash, "^sha256:[0-9a-f]{64}$", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant))
+    {
+        return Results.BadRequest(new { error = "planHash must be sha256:<64-hex>." });
+    }
+
     var result = await decisionService.ApplyAsync(
         new PackRunApprovalDecisionRequest(runId, approvalId, request.PlanHash, decisionType, request.ActorId, request.Summary),
         cancellationToken).ConfigureAwait(false);