feat: migrate Flask API to Go with JWT auth

pkg/errors/errors.go

@@ -0,0 +1,26 @@
+package errors
+
+type AppError struct {
+	Code    int
+	Message string
+	Details string
+}
+
+func (e *AppError) Error() string {
+	return e.Message
+}
+
+func NewAppError(code int, message, details string) *AppError {
+	return &AppError{
+		Code:    code,
+		Message: message,
+		Details: details,
+	}
+}
+
+var (
+	ErrUnauthorized = NewAppError(401, "Unauthorized", "")
+	ErrNotFound     = NewAppError(404, "Not Found", "")
+	ErrBadRequest   = NewAppError(400, "Bad Request", "")
+	ErrInternal     = NewAppError(500, "Internal Server Error", "")
+)