fix(dashboard): clean up stale position cache on unmatched close events

_handle_close was not clearing _current_positions when no matching OPEN
trade was found in DB, causing all subsequent entries for the same
symbol+direction to be silently skipped. Also add PYTHONUNBUFFERED=1
and python -u to make log parser crashes visible in docker logs.

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

docker-compose.yml

@@ -23,6 +23,7 @@ services:
     restart: unless-stopped
     environment:
       - TZ=Asia/Seoul
+      - PYTHONUNBUFFERED=1
       - LOG_DIR=/app/logs
       - DB_PATH=/app/data/dashboard.db
       - POLL_INTERVAL=5