换仓评估修复：沉没成本不参与决策

之前逻辑：expected_gain > locked_loss * 1.5 → 沉没成本谬误
错的：把已发生的亏损当成了交易成本

修复后：
1. 已亏损是沉没成本，卖不卖都已损失，不参与决策
2. 只比较持有 old 票的未来预期 vs 换到 new 票的未来预期
3. 深套票(<-15%)默认=死钱，继续持有预期≈-5%~0%
4. 目标票(RR>=3+买入信号)才有换仓资格
5. 最多卖2只、不超过总资产50%
6. 优先选亏损比例小、市值大的（效率高）

输出示例（已实测）：
  换仓建议：卖双一科技(亏-15.9%)；阿里(亏-21.7%)→腾69k→买海博思创1手(53k)
  理由：已深套，回本需涨19~28%不现实，死钱换有信号票，止损-3%可控，+17%空间明确

data/portfolio.json

@@ -54,8 +54,8 @@
         "action_note": "深套持有",
         "timing_signal": "持有"
       },
-      "price": 7.59,
-      "change_pct": -3.68
+      "price": 7.66,
+      "change_pct": -2.79
     },
     {
       "code": "600739",
@@ -167,8 +167,8 @@
         "action_note": "深套持有",
         "timing_signal": "持有"
       },
-      "price": 98.3,
-      "change_pct": -0.66
+      "price": 98.85,
+      "change_pct": -0.1
     },
     {
       "code": "603259",
@@ -252,8 +252,8 @@
         "action_note": "短炒强趋势持",
         "timing_signal": "持有"
       },
-      "price": 95.6,
-      "change_pct": 9.57
+      "price": 96.3,
+      "change_pct": 10.37
     },
     {
       "code": "02202",
@@ -281,8 +281,8 @@
         "action_note": "深套持有",
         "timing_signal": "持有"
       },
-      "price": 2.35,
-      "change_pct": -2.08
+      "price": 2.37,
+      "change_pct": -1.25
     },
     {
       "code": "02388",
@@ -310,8 +310,8 @@
         "action_note": "",
         "timing_signal": "持有"
       },
-      "price": 46.16,
-      "change_pct": -1.79
+      "price": 46.26,
+      "change_pct": -1.57
     },
     {
       "code": "300750",
@@ -367,8 +367,8 @@
         "action_note": "深套持有",
         "timing_signal": "持有"
       },
-      "price": 74.45,
-      "change_pct": -1.85
+      "price": 74.8,
+      "change_pct": -1.38
     },
     {
       "code": "00700",
@@ -396,8 +396,8 @@
         "action_note": "⚠️盈亏比偏低(1:1.0)，不建议加仓",
         "timing_signal": "持有"
       },
-      "price": 417.4,
-      "change_pct": 0.63
+      "price": 418.8,
+      "change_pct": 0.82
     },
     {
       "code": "00981",
@@ -425,8 +425,8 @@
         "action_note": "",
         "timing_signal": "持有"
       },
-      "price": 84.15,
-      "change_pct": 8.09
+      "price": 85.05,
+      "change_pct": 9.31
     },
     {
       "code": "09868",
@@ -454,8 +454,8 @@
         "action_note": "⚠️盈亏比偏低(1:1.0)，不建议加仓",
         "timing_signal": "持有"
       },
-      "price": 49.58,
-      "change_pct": 0.45
+      "price": 50.0,
+      "change_pct": 1.22
     },
     {
       "code": "600036",
@@ -539,8 +539,8 @@
         "action_note": "⚠️盈亏比偏低(1:1.2)，不建议加仓",
         "timing_signal": "持有"
       },
-      "price": 52.5,
-      "change_pct": -2.05
+      "price": 52.75,
+      "change_pct": -1.59
     },
     {
       "code": "300035",
@@ -652,8 +652,8 @@
         "action_note": "⚠️盈亏比偏低(1:1.0)，不建议加仓",
         "timing_signal": "持有"
       },
-      "price": 41.76,
-      "change_pct": -0.71
+      "price": 41.84,
+      "change_pct": -0.52
     },
     {
       "code": "600563",