feat: enhance tracing with field attributes and warn logging across all handlers

Add repo_id, finding_id, and filter fields to tracing::instrument attributes
for better trace correlation in SigNoz. Replace all silently swallowed errors
(Err(_) => Vec::new()) with tracing::warn! logging across mod.rs, dast.rs,
graph.rs handlers. Add stage-level spans with .instrument() to pipeline
orchestrator for visibility into scan phases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compliance-agent/src/api/handlers/chat.rs

@@ -17,7 +17,7 @@ use super::ApiResponse;
 type AgentExt = Extension<Arc<ComplianceAgent>>;
 
 /// POST /api/v1/chat/:repo_id — Send a chat message with RAG context
-#[tracing::instrument(skip_all)]
+#[tracing::instrument(skip_all, fields(repo_id = %repo_id))]
 pub async fn chat(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,
@@ -127,7 +127,7 @@ pub async fn chat(
 }
 
 /// POST /api/v1/chat/:repo_id/build-embeddings — Trigger embedding build
-#[tracing::instrument(skip_all)]
+#[tracing::instrument(skip_all, fields(repo_id = %repo_id))]
 pub async fn build_embeddings(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,
@@ -228,7 +228,7 @@ pub async fn build_embeddings(
 }
 
 /// GET /api/v1/chat/:repo_id/status — Get latest embedding build status
-#[tracing::instrument(skip_all)]
+#[tracing::instrument(skip_all, fields(repo_id = %repo_id))]
 pub async fn embedding_status(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,