Fix: entry token 만료 기반으로 stale waiting room 판단

타임아웃 대신 Redis entry token 존재 여부로 판단:
- pending token이 Redis에 남아있음 → 정상 로딩 중, 방 보존
- pending token이 없음 (만료/소비) → abandoned 확정, 즉시 정리

정상 로딩 중인 파티원의 방을 보호하면서도
강제 종료 유저의 즉각적 복구 가능.

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

internal/bossraid/repository.go

@@ -64,14 +64,13 @@ func (r *Repository) CountActiveByUsername(username string) (int64, error) {
 	return count, err
 }
 
-// FindStaleWaitingRoomsByUsername returns waiting rooms containing the given username
-// that were created before the threshold.
-func (r *Repository) FindStaleWaitingRoomsByUsername(username string, threshold time.Time) ([]BossRoom, error) {
+// FindWaitingRoomsByUsername returns all waiting rooms containing the given username.
+func (r *Repository) FindWaitingRoomsByUsername(username string) ([]BossRoom, error) {
 	escaped := strings.NewReplacer("%", "\\%", "_", "\\_").Replace(username)
 	search := `"` + escaped + `"`
 	var rooms []BossRoom
-	err := r.db.Where("status = ? AND players LIKE ? AND created_at < ?",
-		StatusWaiting, "%"+search+"%", threshold).
+	err := r.db.Where("status = ? AND players LIKE ?",
+		StatusWaiting, "%"+search+"%").
 		Find(&rooms).Error
 	return rooms, err
 }