feat: add OpenTelemetry trace spans to all handlers and pipeline functions

Add #[tracing::instrument(skip_all)] to 44 functions:
- 19 API handlers in mod.rs
- 3 chat handlers, 6 DAST handlers, 7 graph handlers
- 2 pipeline orchestrator functions
- 7 scanner functions (sbom, semgrep, gitleaks, cve, lint, patterns)

This generates trace spans for SigNoz visibility into request
latency, scan pipeline stages, and error tracking.

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

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

@@ -33,6 +33,7 @@ fn default_search_limit() -> usize {
 }
 
 /// GET /api/v1/graph/:repo_id — Full graph data
+#[tracing::instrument(skip_all)]
 pub async fn get_graph(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,
@@ -88,6 +89,7 @@ pub async fn get_graph(
 }
 
 /// GET /api/v1/graph/:repo_id/nodes — List nodes (paginated)
+#[tracing::instrument(skip_all)]
 pub async fn get_nodes(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,
@@ -109,6 +111,7 @@ pub async fn get_nodes(
 }
 
 /// GET /api/v1/graph/:repo_id/communities — List detected communities
+#[tracing::instrument(skip_all)]
 pub async fn get_communities(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,
@@ -158,6 +161,7 @@ pub struct CommunityInfo {
 }
 
 /// GET /api/v1/graph/:repo_id/impact/:finding_id — Impact analysis
+#[tracing::instrument(skip_all)]
 pub async fn get_impact(
     Extension(agent): AgentExt,
     Path((repo_id, finding_id)): Path<(String, String)>,
@@ -179,6 +183,7 @@ pub async fn get_impact(
 }
 
 /// GET /api/v1/graph/:repo_id/search — BM25 symbol search
+#[tracing::instrument(skip_all)]
 pub async fn search_symbols(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,
@@ -211,6 +216,7 @@ pub async fn search_symbols(
 }
 
 /// GET /api/v1/graph/:repo_id/file-content — Read source file from cloned repo
+#[tracing::instrument(skip_all)]
 pub async fn get_file_content(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,
@@ -272,6 +278,7 @@ pub struct FileContent {
 }
 
 /// POST /api/v1/graph/:repo_id/build — Trigger graph rebuild
+#[tracing::instrument(skip_all)]
 pub async fn trigger_build(
     Extension(agent): AgentExt,
     Path(repo_id): Path<String>,