feat(onboarding): scan-trigger endpoint + wizard Run-Scan button

Complete the onboard -> scan -> results loop in-UI:
- POST /api/v1/targets/{id}/scan (404s unknown targets) spawns run_scan, which
  dispatches to the unified pipeline under UNIFIED_PIPELINE.
- Wizard Done step gains a "Run scan" button (server fn trigger_target_scan)
  with inline status, so a user can onboard and kick off a scan without curl.

Passes fmt + clippy -D warnings (agent, dashboard server + web).

Closes #126, #127. Refs #131, #133, #118.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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

@@ -348,3 +348,43 @@ pub async fn detect_target(
         page: None,
     }))
 }
+
+/// POST /api/v1/targets/{id}/scan — trigger a scan for the target.
+///
+/// Dispatches to the unified pipeline when `UNIFIED_PIPELINE` is set (else the
+/// legacy path). Runs in the background and returns immediately.
+#[tracing::instrument(skip_all, fields(target_id = %id))]
+pub async fn trigger_target_scan(
+    Extension(agent): AgentExt,
+    tenant: TenantCtx,
+    Path(id): Path<String>,
+) -> Result<Json<serde_json::Value>, StatusCode> {
+    let oid = parse_oid(&id)?;
+    let db = tenant_db(&agent, &tenant).await?;
+    // 404 if the target doesn't exist for this tenant.
+    if db
+        .onboarded_targets()
+        .find_one(doc! { "_id": oid })
+        .await
+        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?
+        .is_none()
+    {
+        return Err(StatusCode::NOT_FOUND);
+    }
+
+    let agent_clone = (*agent).clone();
+    let tenant_id = tenant.0.tenant_id.clone();
+    tokio::spawn(async move {
+        if let Err(e) = agent_clone
+            .run_scan(
+                &tenant_id,
+                &id,
+                compliance_core::models::ScanTrigger::Manual,
+            )
+            .await
+        {
+            tracing::error!("Manual target scan failed for {id}: {e}");
+        }
+    });
+    Ok(Json(serde_json::json!({ "status": "scan_triggered" })))
+}

compliance-agent/src/api/routes.rs

@@ -48,6 +48,10 @@ pub fn build_router() -> Router {
             "/api/v1/targets/{id}/detect",
             post(handlers::onboarding::detect_target),
         )
+        .route(
+            "/api/v1/targets/{id}/scan",
+            post(handlers::onboarding::trigger_target_scan),
+        )
         .route("/api/v1/findings", get(handlers::list_findings))
         .route("/api/v1/findings/{id}", get(handlers::get_finding))
         .route(