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/routes/content_routes.py

@@ -77,12 +77,22 @@ def _resolve_recipient(payload: dict, visibility: str, current_user_id: int):
     return recipient, None
 
 
-def _predict_and_decide(text: str) -> tuple[dict, float, bool]:
+def _predict_and_decide(text: str, user_credit: int = 100) -> tuple[dict, float, bool]:
+    """根据用户信誉分调整阈值系数。信誉分越高，阈值越高（降低敏感度）"""
     clf = _ensure_ready()
     result = clf.predict(text)
-    threshold = float(_get_config().spam_threshold)
-    blocked = float(result["spam_probability"]) >= threshold
-    return result, threshold, blocked
+    base_threshold = float(_get_config().spam_threshold)
+
+    # 信誉分影响阈值系数：credit 0-200，默认100
+    # credit > 100：阈值提高（降低敏感度，减少误判）
+    # credit < 100：阈值降低（提高敏感度，加强拦截）
+    # 系数范围：0.85 - 1.15
+    credit_factor = 1.0 + (user_credit - 100) * 0.0015  # 每10分变化1.5%
+    credit_factor = max(0.85, min(1.15, credit_factor))
+
+    adjusted_threshold = base_threshold * credit_factor
+    blocked = float(result["spam_probability"]) >= adjusted_threshold
+    return result, adjusted_threshold, blocked
 
 
 @content_bp.post("/publish")
@@ -103,7 +113,7 @@ def publish_text():
     if err:
         return fail(err, 400)
 
-    result, threshold, blocked = _predict_and_decide(text)
+    result, threshold, blocked = _predict_and_decide(text, user.credit_score or 100)
 
     post = ContentPost(
         user_id=user.id,
@@ -134,6 +144,13 @@ def publish_text():
 
     db.session.add(post)
     db.session.add(detect_log)
+
+    # 发布成功（未被拦截），小幅增加信誉分；被拦截则小幅减少
+    if not blocked:
+        user.credit_score = min(200, (user.credit_score or 100) + 1)
+    else:
+        user.credit_score = max(0, (user.credit_score or 100) - 2)
+
     db.session.commit()
 
     feedback = "发布成功" if not blocked else "疑似垃圾信息，系统已拦截，可提交申诉"
@@ -171,7 +188,7 @@ def edit_post(post_id: int):
     if err:
         return fail(err, 400)
 
-    result, threshold, blocked = _predict_and_decide(text)
+    result, threshold, blocked = _predict_and_decide(text, user.credit_score or 100)
 
     post.text = result["text"]
     post.visibility = visibility