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/dast.rs

@@ -63,7 +63,10 @@ pub async fn list_targets(
         .await
     {
         Ok(cursor) => collect_cursor_async(cursor).await,
-        Err(_) => Vec::new(),
+        Err(e) => {
+            tracing::warn!("Failed to fetch DAST targets: {e}");
+            Vec::new()
+        }
     };
 
     Ok(Json(ApiResponse {
@@ -101,7 +104,7 @@ pub async fn add_target(
 }
 
 /// POST /api/v1/dast/targets/:id/scan — Trigger DAST scan
-#[tracing::instrument(skip_all)]
+#[tracing::instrument(skip_all, fields(target_id = %id))]
 pub async fn trigger_scan(
     Extension(agent): AgentExt,
     Path(id): Path<String>,
@@ -163,7 +166,10 @@ pub async fn list_scan_runs(
         .await
     {
         Ok(cursor) => collect_cursor_async(cursor).await,
-        Err(_) => Vec::new(),
+        Err(e) => {
+            tracing::warn!("Failed to fetch DAST scan runs: {e}");
+            Vec::new()
+        }
     };
 
     Ok(Json(ApiResponse {
@@ -196,7 +202,10 @@ pub async fn list_findings(
         .await
     {
         Ok(cursor) => collect_cursor_async(cursor).await,
-        Err(_) => Vec::new(),
+        Err(e) => {
+            tracing::warn!("Failed to fetch DAST findings: {e}");
+            Vec::new()
+        }
     };
 
     Ok(Json(ApiResponse {
@@ -207,7 +216,7 @@ pub async fn list_findings(
 }
 
 /// GET /api/v1/dast/findings/:id — Finding detail with evidence
-#[tracing::instrument(skip_all)]
+#[tracing::instrument(skip_all, fields(finding_id = %id))]
 pub async fn get_finding(
     Extension(agent): AgentExt,
     Path(id): Path<String>,