feat(yggdrasil): implement standard error responses and UUID format improvements

- Add YggdrasilErrorResponse struct and standard error codes for protocol compliance
- Change UUID storage from varchar(36) to varchar(32) for unsigned format
- Add utility functions: GenerateUUID, FormatUUIDToNoDash, RandomHex
- Support unsigned query parameter in GetProfileByUUID endpoint
- Improve refresh token response with available profiles list
- Fix key pair retrieval to use correct database column (rsa_private_key)
- Update UUID validator to accept both 32-char and 36-char formats
- Add SignStringWithProfileRSA method for profile-specific signing
- Fix profile assignment validation in refresh token flow

internal/service/yggdrasil_serialization_service.go

@@ -14,6 +14,8 @@ import (
 type SerializationService interface {
 	// SerializeProfile 序列化档案为Yggdrasil格式
 	SerializeProfile(ctx context.Context, profile model.Profile) map[string]interface{}
+	// SerializeProfileWithUnsigned 序列化档案为Yggdrasil格式（支持unsigned参数）
+	SerializeProfileWithUnsigned(ctx context.Context, profile model.Profile, unsigned bool) map[string]interface{}
 	// SerializeUser 序列化用户为Yggdrasil格式
 	SerializeUser(ctx context.Context, user *model.User, uuid string) map[string]interface{}
 }
@@ -45,8 +47,13 @@ func NewSerializationService(
 	}
 }
 
-// SerializeProfile 序列化档案为Yggdrasil格式
+// SerializeProfile 序列化档案为Yggdrasil格式（默认返回签名）
 func (s *yggdrasilSerializationService) SerializeProfile(ctx context.Context, profile model.Profile) map[string]interface{} {
+	return s.SerializeProfileWithUnsigned(ctx, profile, false)
+}
+
+// SerializeProfileWithUnsigned 序列化档案为Yggdrasil格式（支持unsigned参数）
+func (s *yggdrasilSerializationService) SerializeProfileWithUnsigned(ctx context.Context, profile model.Profile, unsigned bool) map[string]interface{} {
 	// 创建基本材质数据
 	texturesMap := make(map[string]interface{})
 	textures := map[string]interface{}{
@@ -99,26 +106,36 @@ func (s *yggdrasilSerializationService) SerializeProfile(ctx context.Context, pr
 	}
 
 	textureData := base64.StdEncoding.EncodeToString(bytes)
-	signature, err := s.signatureService.SignStringWithSHA1withRSA(textureData)
-	if err != nil {
-		s.logger.Error("签名textures失败",
-			zap.Error(err),
-			zap.String("profileUUID", profile.UUID),
-		)
-		return nil
+
+	// 只有在 unsigned=false 时才签名
+	var signature string
+	if !unsigned {
+		signature, err = s.signatureService.SignStringWithSHA1withRSA(textureData)
+		if err != nil {
+			s.logger.Error("签名textures失败",
+				zap.Error(err),
+				zap.String("profileUUID", profile.UUID),
+			)
+			return nil
+		}
+	}
+
+	// 构建属性
+	property := Property{
+		Name:  "textures",
+		Value: textureData,
+	}
+
+	// 只有在 unsigned=false 时才添加签名
+	if !unsigned {
+		property.Signature = signature
 	}
 
 	// 构建结果
 	data := map[string]interface{}{
-		"id":   profile.UUID,
-		"name": profile.Name,
-		"properties": []Property{
-			{
-				Name:      "textures",
-				Value:     textureData,
-				Signature: signature,
-			},
-		},
+		"id":         profile.UUID,
+		"name":       profile.Name,
+		"properties": []Property{property},
 	}
 	return data
 }