fix: FR score 0~5 only, no negative scores

Direction is already decided. FR layer measures how favorable
the funding rate is for that direction. Unfavorable = 0, not negative.

backend/signal_engine.py

@@ -522,13 +522,14 @@ class SymbolState:
             fr_abs = abs(funding_rate)
             # 线性映射: raw = (|当前FR| / 历史最大FR) × 5, clamp到5
             raw_score = min(fr_abs / max_fr * 5.0, 5.0)
-            # 方向判断: 逆向操作加分，顺向操作减分
-            # 做多+FR负(空头付钱)=逆向=好 → 正分
-            # 做多+FR正(多头付钱)=顺向=坏 → 负分
+            # FR评估"资金费率对当前方向有多有利"，0~5分，不扣分
+            # 做多+FR负(空头付费给多头)=有利 → 给分
+            # 做空+FR正(多头付费给空头)=有利 → 给分
+            # 其他情况(FR方向不利) → 0分
             if (direction == "LONG" and funding_rate < 0) or (direction == "SHORT" and funding_rate > 0):
-                fr_score = round(raw_score, 2)   # 逆向操作，加分
+                fr_score = round(raw_score, 2)   # 有利，给分
             else:
-                fr_score = round(-raw_score, 2)   # 顺向操作，减分
+                fr_score = 0.0  # 不利，不给分也不扣分
 
         # 4) 确认层（15分）
         confirmation_score = 15 if (