fix(trader): record trade and snapshot prices at full precision

Rounding to cents made trade logs irreproducible for low-priced lines
(HK ETFs in USD, A-shares): replaying a log drifted up to $200 from the
recorded cash.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

trader.py

@@ -523,7 +523,7 @@ def compute_trades(holdings: dict, cash: float, target_weights: dict,
             "shares_delta": int(round(delta)) if integer_shares else round(delta, 4),
             "direction": "BUY" if delta > 0 else "SELL",
             "est_value": round(trade_value, 2),
-            "price": round(price, 2),
+            "price": round(price, 6),
             "target_shares": int(round(target_shares)) if integer_shares else round(target_shares, 4),
             "current_shares": int(current_shares) if integer_shares else round(current_shares, 4),
         })
@@ -620,7 +620,7 @@ def execute_trades(state: dict, trades: list[dict], prices: dict,
             "action": "BUY" if delta > 0 else "SELL",
             "ticker": ticker,
             "shares": abs(delta) if integer_shares else round(abs(delta), 4),
-            "price": round(price, 2),
+            "price": round(price, 6),
             "value": round(cost, 2),
             "commission": round(commission, 2),
         })
@@ -650,7 +650,7 @@ def record_daily_snapshot(state: dict, date_str: str, prices: dict,
         p = prices.get(ticker, 0.0)
         positions[ticker] = {
             "shares": shares,
-            "price": round(p, 2),
+            "price": round(p, 6),
             "value": round(shares * p, 2),
         }
 
@@ -662,7 +662,7 @@ def record_daily_snapshot(state: dict, date_str: str, prices: dict,
             "action": t["direction"],
             "ticker": t["ticker"],
             "shares": abs(t["shares_delta"]),
-            "price": round(p, 2),
+            "price": round(p, 6),
             "value": round(abs(t["shares_delta"]) * p, 2),
         })