feat: add per-symbol strategy params with sweep-optimized values

Support per-symbol strategy parameters (ATR_SL_MULT_XRPUSDT, etc.)
via env vars, falling back to global defaults. Sweep results:
- XRPUSDT: SL=1.5 TP=4.0 ADX=30 (PF 2.39, Sharpe 61.0)
- TRXUSDT: SL=1.0 TP=4.0 ADX=30 (PF 3.87, Sharpe 62.8)
- DOGEUSDT: SL=2.0 TP=2.0 ADX=30 (PF 1.80, Sharpe 44.1)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env.example

@@ -8,11 +8,25 @@ DISCORD_WEBHOOK_URL=
 ML_THRESHOLD=0.55
 NO_ML_FILTER=true
 MAX_SAME_DIRECTION=2
+# Global defaults (fallback when no per-symbol override)
 ATR_SL_MULT=2.0
 ATR_TP_MULT=2.0
 SIGNAL_THRESHOLD=3
 ADX_THRESHOLD=25
 VOL_MULTIPLIER=2.5
+
+# Per-symbol strategy params (2026-03-17 sweep optimized)
+ATR_SL_MULT_XRPUSDT=1.5
+ATR_TP_MULT_XRPUSDT=4.0
+ADX_THRESHOLD_XRPUSDT=30
+
+ATR_SL_MULT_TRXUSDT=1.0
+ATR_TP_MULT_TRXUSDT=4.0
+ADX_THRESHOLD_TRXUSDT=30
+
+ATR_SL_MULT_DOGEUSDT=2.0
+ATR_TP_MULT_DOGEUSDT=2.0
+ADX_THRESHOLD_DOGEUSDT=30
 DASHBOARD_API_URL=http://10.1.10.24:8000
 BINANCE_TESTNET_API_KEY=
 BINANCE_TESTNET_API_SECRET=