Fix fee tier recalculation for historical backtests

Server: recalc endpoint now checks HISTORICAL_DIR as fallback
when file not found in BACKTEST_DIR. Previously historical backtests
returned "not found" on recalc.

Frontend: renderBTDetail now accepts pnl_net/pnl_net_pct from
recalc response (the endpoint returns pnl_net not pnl).

Verified: VIP 0 → VIP 6 on OBI historical backtest changes
net PnL from 54.31% to 66.57% with fees dropping $18.10 → $5.85.

dashboard/server.py

@@ -204,6 +204,8 @@ async def get_backtest(name: str):
 async def recalc_backtest(name: str, fee_tier: int = 0, staking_tier: str = "none"):
     """Recalculate backtest PnL with different fee tier."""
     fpath = os.path.join(BACKTEST_DIR, f"{name}.json")
+    if not os.path.exists(fpath):
+        fpath = os.path.join(HISTORICAL_DIR, f"{name}.json")
     if not os.path.exists(fpath):
         return JSONResponse({"error": "not found"}, status_code=404)
     with open(fpath) as f: