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/repository/profile_repository.go

@@ -131,8 +131,8 @@ func (r *profileRepository) GetKeyPair(ctx context.Context, profileId string) (*
 
 	var profile model.Profile
 	result := r.db.WithContext(ctx).
-		Select("key_pair").
-		Where("id = ?", profileId).
+		Select("rsa_private_key").
+		Where("uuid = ?", profileId).
 		First(&profile)
 
 	if result.Error != nil {
@@ -142,7 +142,9 @@ func (r *profileRepository) GetKeyPair(ctx context.Context, profileId string) (*
 		return nil, fmt.Errorf("获取key pair失败: %w", result.Error)
 	}
 
-	return &model.KeyPair{}, nil
+	return &model.KeyPair{
+		PrivateKey: profile.RSAPrivateKey,
+	}, nil
 }
 
 func (r *profileRepository) UpdateKeyPair(ctx context.Context, profileId string, keyPair *model.KeyPair) error {
@@ -154,12 +156,9 @@ func (r *profileRepository) UpdateKeyPair(ctx context.Context, profileId string,
 	}
 
 	return r.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
-		result := tx.Table("profiles").
-			Where("id = ?", profileId).
-			UpdateColumns(map[string]interface{}{
-				"private_key": keyPair.PrivateKey,
-				"public_key":  keyPair.PublicKey,
-			})
+		result := tx.Model(&model.Profile{}).
+			Where("uuid = ?", profileId).
+			Update("rsa_private_key", keyPair.PrivateKey)
 
 		if result.Error != nil {
 			return fmt.Errorf("更新 keyPair 失败: %w", result.Error)