feat(metrics): Add new histograms for chunk latency, results, and sources in AdvisoryAiMetrics

feat(telemetry): Record chunk latency, result count, and source count in AdvisoryAiTelemetry

fix(endpoint): Include telemetry source count in advisory chunks endpoint response

test(metrics): Enhance WebServiceEndpointsTests to validate new metrics for chunk latency, results, and sources

refactor(tests): Update test utilities for Deno language analyzer tests

chore(tests): Add performance tests for AdvisoryGuardrail with scenarios and blocked phrases

docs: Archive Sprint 137 design document for scanner and surface enhancements

src/Concelier/StellaOps.Concelier.WebService/Program.cs

@@ -913,6 +913,7 @@ var advisoryChunksEndpoint = app.MapGet("/advisories/{advisoryKey}/chunks", asyn
         buildResult.Response.Truncated,
         cacheHit,
         observations.Length,
+        buildResult.Telemetry.SourceCount,
         buildResult.Response.Chunks.Count,
         duration,
         guardrailCounts));