fix: replace silent json.Encode with error-logging pattern across all handlers

backend/main.go

@@ -151,10 +151,12 @@ func healthCheckHandler(w http.ResponseWriter, r *http.Request) {
 	} else {
 		w.WriteHeader(http.StatusOK)
 	}
-	_ = json.NewEncoder(w).Encode(map[string]any{
+	if err := json.NewEncoder(w).Encode(map[string]any{
 		"status":   status,
 		"services": services,
-	})
+	}); err != nil {
+		log.Printf("Failed to encode JSON response: %v", err)
+	}
 }
 
 func main() {