fix: BossRoom soft delete → hard delete + 프로필 자동 생성

- BossRoom 삭제 시 Unscoped() hard delete로 변경하여 unique index 충돌 방지
- GetProfile에서 프로필 없으면 기본값으로 자동 생성

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

internal/bossraid/repository.go

@@ -208,8 +208,9 @@ func (r *Repository) ResetRoomSlot(sessionName string) error {
 
 // DeleteRoomBySessionName removes BossRoom records for a given session name.
 // Used during ResetRoom to prevent duplicate session_name conflicts on next entry.
+// Unscoped to perform hard delete — soft delete would leave the unique index occupied.
 func (r *Repository) DeleteRoomBySessionName(sessionName string) error {
-	return r.db.Where("session_name = ?", sessionName).Delete(&BossRoom{}).Error
+	return r.db.Unscoped().Where("session_name = ?", sessionName).Delete(&BossRoom{}).Error
 }
 
 // ResetStaleSlots clears instanceID for slots with stale heartbeats