Update project structure and enhance frontend functionality

- Added a new AGENTS.md file to document the project structure and conventions.
- Updated .gitignore to include node_modules and refined cursor rules.
- Introduced new backend and frontend components for improved map interactions, including context menus and controls.
- Enhanced API composables for better admin and authentication functionalities.
- Refactored existing components for cleaner code and improved user experience.
- Updated README.md to clarify production asset serving and user setup instructions.

internal/app/response/response.go

@@ -0,0 +1,25 @@
+package response
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+// JSON writes v as JSON with the given status code.
+func JSON(rw http.ResponseWriter, status int, v any) {
+	rw.Header().Set("Content-Type", "application/json")
+	rw.WriteHeader(status)
+	if v != nil {
+		_ = json.NewEncoder(rw).Encode(v)
+	}
+}
+
+// JSONError writes an error response in standard format: {"error": "message", "code": "CODE"}.
+func JSONError(rw http.ResponseWriter, status int, msg string, code string) {
+	rw.Header().Set("Content-Type", "application/json")
+	rw.WriteHeader(status)
+	_ = json.NewEncoder(rw).Encode(map[string]string{
+		"error": msg,
+		"code":  code,
+	})
+}