现金冻结修复：price_monitor不再重算cash

根因：price_monitor每2分钟用av+fz重算cash，
但av/fz是旧数据(含法拉电子卖出前冻结)，
覆盖了Dad交易截图后的正确现金92,679。

修复：
1. price_monitor只更新market_value，不碰cash
2. cash设回正确值92,678.85（含法拉电子+18,920）
3. 加cash_history追踪每次修改

data/portfolio.json

@@ -649,15 +649,15 @@
       "_currency": "CNY"
     }
   ],
-  "cash": 113240.25,
+  "cash": 92678.85,
   "total_market_value": 835552.6,
-  "total_assets": 948792.85,
+  "total_assets": 928231.45,
   "total_pl": 0,
-  "position_pct": 88.06,
-  "updated_at": "2026-06-29 22:03",
+  "position_pct": 90.02,
+  "updated_at": "2026-06-29 22:23:47",
   "source": "/home/hmo/stocks/holding.xls",
   "frozen_cash": 39481.4,
-  "available_cash": 73758.85,
+  "available_cash": 92678.85,
   "frozen": 39481.4,
   "total_cash": 132145.6,
   "cash_updated_at": "2026-06-29 12:34",
@@ -672,11 +672,20 @@
       "timestamp": "2026-06-29 10:43"
     }
   ],
-  "total_mv": 855311.0,
+  "total_mv": 835552.6,
   "note": "cash fixed from screenshot 6/29, prices=CNY",
   "currency": "CNY",
   "last_verified_at": "2026-06-29 22:20",
   "_total_mv": 835552.6,
   "_total_cash": 113240.25,
-  "_total_assets": 948792.85
+  "_total_assets": 948792.85,
+  "cash_history": [
+    {
+      "time": "2026-06-29 22:23:47",
+      "cash": 92678.85,
+      "frozen": 39481.4,
+      "source": "manual:post-法拉电子-sell-100shares@189.2",
+      "formula": "初始可用73758.85+法拉电子18920"
+    }
+  ]
 }