feat: add Discord webhook notifications to MTF dry-run bot

Sends alerts for: bot start, virtual entry (LONG/SHORT with SL/TP),
and SL/TP exits with PnL. Uses existing DiscordNotifier via
DISCORD_WEBHOOK_URL from .env. Also added env_file to mtf-bot
docker-compose service.

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

main_mtf.py

@@ -2,10 +2,13 @@
 
 import asyncio
 import signal as sig
+from dotenv import load_dotenv
 from loguru import logger
 from src.mtf_bot import MTFPullbackBot
 from src.logger_setup import setup_logger
 
+load_dotenv()
+
 
 async def main():
     setup_logger(log_level="INFO")