feat: 计仓改为固定手数/固定金额，推荐过滤与CTP保证金，下单与持仓UI优化

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

trading_context.py

@@ -14,7 +14,21 @@ def get_trading_mode(get_setting: Callable[[str, str], str]) -> str:
 
 def get_sizing_mode(get_setting: Callable[[str, str], str]) -> str:
     from position_sizing import normalize_sizing_mode
-    return normalize_sizing_mode(get_setting("position_sizing_mode", "risk"))
+    return normalize_sizing_mode(get_setting("position_sizing_mode", "fixed"))
+
+
+def get_fixed_lots(get_setting: Callable[[str, str], str]) -> int:
+    try:
+        return max(1, int(float(get_setting("fixed_lots", "1") or 1)))
+    except (TypeError, ValueError):
+        return 1
+
+
+def get_fixed_amount(get_setting: Callable[[str, str], str]) -> float:
+    try:
+        return max(1.0, float(get_setting("fixed_amount", "5000") or 5000))
+    except (TypeError, ValueError):
+        return 5000.0
 
 
 def get_risk_percent(get_setting: Callable[[str, str], str]) -> float: