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/Signals/StellaOps.Signals/Program.cs

@@ -83,6 +83,7 @@ builder.Services.AddRouting(options => options.LowercaseUrls = true);
 
 builder.Services.AddSingleton<ICallgraphRepository, InMemoryCallgraphRepository>();
 builder.Services.AddSingleton<ICallgraphNormalizationService, CallgraphNormalizationService>();
+builder.Services.AddSingleton<ICallGraphProjectionRepository, InMemoryCallGraphProjectionRepository>();
 
 // Configure callgraph artifact storage based on driver
 if (bootstrap.Storage.IsRustFsDriver())
@@ -117,6 +118,7 @@ builder.Services.AddSingleton<ICallgraphParser>(new SimpleJsonCallgraphParser("p
 builder.Services.AddSingleton<ICallgraphParser>(new SimpleJsonCallgraphParser("go"));
 builder.Services.AddSingleton<ICallgraphParserResolver, CallgraphParserResolver>();
 builder.Services.AddSingleton<ICallgraphIngestionService, CallgraphIngestionService>();
+builder.Services.AddSingleton<ICallGraphSyncService, CallGraphSyncService>();
 builder.Services.AddSingleton<IReachabilityCache>(sp =>
 {
     var options = sp.GetRequiredService<IOptions<SignalsOptions>>().Value;
@@ -197,6 +199,7 @@ builder.Services.AddSingleton<IEventsPublisher>(sp =>
         eventBuilder);
 });
 builder.Services.AddSingleton<IReachabilityScoringService, ReachabilityScoringService>();
+builder.Services.AddSingleton<IScoreExplanationService, ScoreExplanationService>(); // Sprint: SPRINT_3800_0001_0002
 builder.Services.AddSingleton<IRuntimeFactsProvenanceNormalizer, RuntimeFactsProvenanceNormalizer>();
 builder.Services.AddSingleton<IRuntimeFactsIngestionService, RuntimeFactsIngestionService>();
 builder.Services.AddSingleton<IReachabilityUnionIngestionService, ReachabilityUnionIngestionService>();