feat(ECR-011): 昵称、首页贴士与档案 Self 唯一/合盘交叉校验

每账号仅一条 self（migration 40902）；合盘只选 TA；账号昵称可改；首页穿衣/颜色/养生贴士。

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/internal/handler/profile.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"errors"
 	"net/http"
 	"time"
 
@@ -56,6 +57,10 @@ func (h *ProfileHandler) Create(c *gin.Context) {
 		RelationType: req.RelationType, BirthTime: req.BirthTime, BirthPlace: req.BirthPlace,
 	})
 	if err != nil {
+		if errors.Is(err, profile.ErrSelfExists) {
+			response.Fail(c, http.StatusConflict, 40902, err.Error())
+			return
+		}
 		response.Fail(c, http.StatusBadRequest, 30001, err.Error())
 		return
 	}