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/types/common.go

@@ -154,7 +154,7 @@ type TextureInfo struct {
 // ProfileInfo 角色信息
 // @Description Minecraft档案信息
 type ProfileInfo struct {
-	UUID       string     `json:"uuid" example:"550e8400-e29b-41d4-a716-446655440000"`
+	UUID       string     `json:"uuid" example:"550e8400e29b41d4a716446655440000"`
 	UserID     int64      `json:"user_id" example:"1"`
 	Name       string     `json:"name" example:"PlayerName"`
 	SkinID     *int64     `json:"skin_id,omitempty" example:"1"`