feat: 删除用户前自动转移个人配方到管理员账号

配方名后附加用户名（如"头疗（小明）"），审计日志记录转移数量。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/main.py

@@ -1107,10 +1107,21 @@ def delete_user(user_id: int, user=Depends(require_role("admin"))):
     if not target:
         conn.close()
         raise HTTPException(404, "User not found")
+    # Transfer personal diary recipes to admin before deletion
+    target_name = target["display_name"] or target["username"]
+    diaries = conn.execute("SELECT id, name FROM user_diary WHERE user_id = ?", (user_id,)).fetchall()
+    if diaries:
+        for d in diaries:
+            new_name = f"{d['name']}（{target_name}）"
+            conn.execute("UPDATE user_diary SET user_id = ?, name = ? WHERE id = ?",
+                         (user["id"], new_name, d["id"]))
     snapshot = dict(target)
     conn.execute("DELETE FROM users WHERE id = ?", (user_id,))
+    detail = dict(snapshot)
+    if diaries:
+        detail["transferred_diary_count"] = len(diaries)
     log_audit(conn, user["id"], "delete_user", "user", user_id, target["username"],
-              json.dumps(snapshot, ensure_ascii=False))
+              json.dumps(detail, ensure_ascii=False))
     conn.commit()
     conn.close()
     return {"ok": True}