feat: add data validation and structured logging

internal/models/user.go

@@ -20,9 +20,9 @@ type User struct {
 
 // RegisterRequest определяет структуру JSON-запроса на регистрацию
 type RegisterRequest struct {
-	Username string `json:"username"`
-	Email    string `json:"email"`
-	Password string `json:"password"`
+	Username string `json:"username" validate:"required,min=3,max=16,alphanum"`
+	Email    string `json:"email" validate:"required,email"`
+	Password string `json:"password" validate:"required,min=8"`
 }
 type Profile struct {
 	ID        int       `json:"-"`