feat(openai): port /responses/compact account support flow (PR #1555)

将 vansour/sub2api#1555 的 OpenAI compact 能力建模手工移植到当前 main：账号
级 compact 状态/auto-force_on-force_off 模式、compact-only 模型映射、调度器
tier 分层（已支持 > 未知 > 已知不支持）、管理后台 compact 主动探测，以及对应
i18n/状态徽章。普通 /responses 流量行为不变，无数据库迁移。

backend/internal/service/openai_ws_forwarder.go

@@ -3800,6 +3800,7 @@ func (s *OpenAIGatewayService) SelectAccountByPreviousResponseID(
 	previousResponseID string,
 	requestedModel string,
 	excludedIDs map[int64]struct{},
+	requireCompact bool,
 ) (*AccountSelectionResult, error) {
 	if s == nil {
 		return nil, nil
@@ -3840,11 +3841,16 @@ func (s *OpenAIGatewayService) SelectAccountByPreviousResponseID(
 	if requestedModel != "" && !account.IsModelSupported(requestedModel) {
 		return nil, nil
 	}
-	account = s.recheckSelectedOpenAIAccountFromDB(ctx, account, requestedModel)
+	account = s.recheckSelectedOpenAIAccountFromDB(ctx, account, requestedModel, requireCompact)
 	if account == nil {
 		_ = store.DeleteResponseAccount(ctx, derefGroupID(groupID), responseID)
 		return nil, nil
 	}
+	// 兜底：若上游 compact 能力刚被探测为不支持，但 sticky 还在，需要主动放弃。
+	if requireCompact && openAICompactSupportTier(account) == 0 {
+		_ = store.DeleteResponseAccount(ctx, derefGroupID(groupID), responseID)
+		return nil, nil
+	}
 
 	result, acquireErr := s.tryAcquireAccountSlot(ctx, accountID, account.Concurrency)
 	if acquireErr == nil && result.Acquired {