refactor: Flatten directory structure

Move project files from uzdb/ subdirectory to root directory for cleaner project structure.

Changes:
- Move frontend/ to root
- Move internal/ to root
- Move build/ to root
- Move all config files (go.mod, wails.json, etc.) to root
- Remove redundant uzdb/ subdirectory nesting

Project structure is now:
├── frontend/        # React application
├── internal/        # Go backend
├── build/           # Wails build assets
├── doc/             # Design documentation
├── main.go          # Entry point
└── ...

🤖 Generated with Qoder

internal/utils/response.go

@@ -0,0 +1,102 @@
+package utils
+
+import (
+	"errors"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"go.uber.org/zap"
+
+	"uzdb/internal/config"
+	"uzdb/internal/models"
+)
+
+// ErrorResponse sends an error response
+func ErrorResponse(c *gin.Context, statusCode int, err error, message string) {
+	logger := config.GetLogger()
+	
+	response := models.ErrorResponse{
+		Error:     getErrorCode(err),
+		Message:   message,
+		Timestamp: time.Now(),
+		Path:      c.Request.URL.Path,
+	}
+
+	if message == "" {
+		response.Message = err.Error()
+	}
+
+	// Log the error
+	logger.Error("error response",
+		zap.Int("status_code", statusCode),
+		zap.String("error", response.Error),
+		zap.String("message", response.Message),
+		zap.String("path", response.Path),
+	)
+
+	c.JSON(statusCode, response)
+}
+
+// SuccessResponse sends a success response
+func SuccessResponse(c *gin.Context, data interface{}) {
+	c.JSON(http.StatusOK, models.NewAPIResponse(data))
+}
+
+// CreatedResponse sends a created response
+func CreatedResponse(c *gin.Context, data interface{}) {
+	c.JSON(http.StatusCreated, models.NewAPIResponse(data))
+}
+
+// getErrorCode maps errors to error codes
+func getErrorCode(err error) string {
+	if err == nil {
+		return string(models.CodeSuccess)
+	}
+
+	switch {
+	case errors.Is(err, models.ErrNotFound):
+		return string(models.CodeNotFound)
+	case errors.Is(err, models.ErrValidationFailed):
+		return string(models.CodeValidation)
+	case errors.Is(err, models.ErrUnauthorized):
+		return string(models.CodeUnauthorized)
+	case errors.Is(err, models.ErrForbidden):
+		return string(models.CodeForbidden)
+	case errors.Is(err, models.ErrConnectionFailed):
+		return string(models.CodeConnection)
+	case errors.Is(err, models.ErrQueryFailed):
+		return string(models.CodeQuery)
+	case errors.Is(err, models.ErrEncryptionFailed):
+		return string(models.CodeEncryption)
+	default:
+		return string(models.CodeInternal)
+	}
+}
+
+// WrapError wraps an error with context
+func WrapError(err error, message string) error {
+	if err == nil {
+		return nil
+	}
+	return &wrappedError{
+		err:     err,
+		message: message,
+	}
+}
+
+type wrappedError struct {
+	err     error
+	message string
+}
+
+func (w *wrappedError) Error() string {
+	if w.message != "" {
+		return w.message + ": " + w.err.Error()
+	}
+	return w.err.Error()
+}
+
+func (w *wrappedError) Unwrap() error {
+	return w.err
+}