feat: add Telegram notifications and configurable stop loss

- notify.py: buy/sell/error alerts via upbit_trading_jm_bot
- STOP_LOSS_PCT: trailing stop configurable via .env (default -5%)
- notify_buy/notify_sell called on every trade execution

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -1,6 +1,9 @@
 ACCESS_KEY=
 SECRET_KEY=
 
+# 트레일링 스탑: 최고가 대비 -N% 도달 시 청산
+STOP_LOSS_PCT=5
+
 # 타임 스탑: N시간 경과 후 수익률 M% 미만이면 청산
 TIME_STOP_HOURS=24
 TIME_STOP_MIN_GAIN_PCT=3