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>

dashboard/api/entrypoint.sh

@@ -6,7 +6,7 @@ echo "LOG_DIR=${LOG_DIR:-/app/logs}"
 echo "DB_PATH=${DB_PATH:-/app/data/dashboard.db}"
 
 # 로그 파서를 백그라운드로 실행
-python log_parser.py &
+python -u log_parser.py &
 PARSER_PID=$!
 echo "Log parser started (PID: $PARSER_PID)"