refactor(metrics): remove unused custom query builder

The QueryBuilder component (metric discovery, PromQL editor, label
filtering) was not used in practice. Removes the frontend component,
API functions, types, and corresponding backend handlers (/query,
/discover, /labels) along with the MetricNames prometheus client method.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: janlauber

extensions/metrics/backend/cmd/main.go

@@ -53,9 +53,6 @@ func main() {
 	resourceHandler := handler.NewResource(promClient)
 	appHandler := handler.NewApp(promClient)
 	podsHandler := handler.NewPods(promClient)
-	customHandler := handler.NewCustom(promClient)
-	discoverHandler := handler.NewDiscover(promClient)
-	labelsHandler := handler.NewLabels(promClient)
 	perPodHandler := handler.NewPerPod(promClient)
 
 	// Config-driven dashboard handler
@@ -72,9 +69,6 @@ func main() {
 	mux.HandleFunc("GET /api/v1/app-metrics", appHandler.Handle)
 	mux.HandleFunc("GET /api/v1/pod-breakdown", podsHandler.Handle)
 	mux.HandleFunc("GET /api/v1/per-pod-series", perPodHandler.Handle)
-	mux.HandleFunc("GET /api/v1/query", customHandler.Handle)
-	mux.HandleFunc("GET /api/v1/discover", discoverHandler.Handle)
-	mux.HandleFunc("GET /api/v1/labels", labelsHandler.Handle)
 	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 	})

extensions/metrics/backend/internal/handler/custom.go

@@ -188,6 +188,25 @@ func (h *Dashboard) HandleGraph(w http.ResponseWriter, r *http.Request) {
 	json.NewEncoder(w).Encode(resp)
 }
 
+// seriesLabel builds a human-readable label from metric labels.
+func seriesLabel(labels map[string]string) string {
+	for _, key := range []string{"pod", "container", "namespace", "node", "instance"} {
+		if v, ok := labels[key]; ok && v != "" {
+			return fmt.Sprintf("%s=%s", key, v)
+		}
+	}
+	var parts []string
+	for k, v := range labels {
+		if k != "__name__" {
+			parts = append(parts, fmt.Sprintf("%s=%s", k, v))
+		}
+	}
+	if len(parts) > 0 {
+		return strings.Join(parts, ", ")
+	}
+	return "series"
+}
+
 // renderTemplate executes a Go text/template with the given variables.
 func renderTemplate(expression string, vars map[string]string) (string, error) {
 	tmpl, err := template.New("query").Parse(expression)