feat: add Attestation Chain and Triage Evidence API clients and models

- Implemented Attestation Chain API client with methods for verifying, fetching, and managing attestation chains.
- Created models for Attestation Chain, including DSSE envelope structures and verification results.
- Developed Triage Evidence API client for fetching finding evidence, including methods for evidence retrieval by CVE and component.
- Added models for Triage Evidence, encapsulating evidence responses, entry points, boundary proofs, and VEX evidence.
- Introduced mock implementations for both API clients to facilitate testing and development.

src/Scanner/StellaOps.Scanner.Worker/Program.cs

@@ -113,6 +113,12 @@ if (!string.IsNullOrWhiteSpace(connectionString))
     builder.Services.AddSingleton<ISurfaceManifestPublisher, SurfaceManifestPublisher>();
     builder.Services.AddSingleton<IScanStageExecutor, SurfaceManifestStageExecutor>();
     builder.Services.AddSingleton<IDsseEnvelopeSigner, HmacDsseEnvelopeSigner>();
+
+    // EPSS ingestion job (Sprint: SPRINT_3410_0001_0001)
+    builder.Services.AddOptions<EpssIngestOptions>()
+        .BindConfiguration(EpssIngestOptions.SectionName)
+        .ValidateOnStart();
+    builder.Services.AddHostedService<EpssIngestJob>();
 }
 else
 {