feat: 用户行为信誉分系统

- User 新增 credit_score 字段（0-200，默认100）
- 信誉分影响检测阈值系数：高分降低敏感度，低分提高敏感度
- 发布成功+1分，被拦截-2分；申诉通过+10分，驳回-5分
- 新增手动调整和批量重算信誉分接口
- admin-users 页面显示信誉分进度条，支持编辑调整

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/models.py

@@ -16,6 +16,7 @@ class User(db.Model):
     title = db.Column(db.String(64), default="")
     phone = db.Column(db.String(32), default="")
     is_admin = db.Column(db.Boolean, default=False)
+    credit_score = db.Column(db.Integer, default=100)  # 信誉分 0-200，默认100
     created_at = db.Column(db.DateTime, default=datetime.utcnow)
     updated_at = db.Column(db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
 
@@ -40,6 +41,7 @@ class User(db.Model):
             "title": self.title,
             "phone": self.phone,
             "is_admin": self.is_admin,
+            "credit_score": self.credit_score,
             "created_at": self.created_at.isoformat() if self.created_at else None,
             "updated_at": self.updated_at.isoformat() if self.updated_at else None,
         }