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_gateway_service_test.go

@@ -1107,7 +1107,7 @@ func TestOpenAIStreamingPassthroughMissingTerminalEventReturnsIncompleteError(t
 		_, _ = pw.Write([]byte("data: {\"type\":\"response.in_progress\",\"response\":{}}\n\n"))
 	}()
 
-	_, err := svc.handleStreamingResponsePassthrough(c.Request.Context(), resp, c, &Account{ID: 1}, time.Now())
+	_, err := svc.handleStreamingResponsePassthrough(c.Request.Context(), resp, c, &Account{ID: 1}, time.Now(), "", "")
 	_ = pr.Close()
 	if err == nil || !strings.Contains(err.Error(), "missing terminal event") {
 		t.Fatalf("expected missing terminal event error, got %v", err)
@@ -1139,7 +1139,7 @@ func TestOpenAIStreamingPassthroughResponseDoneWithoutDoneMarkerStillSucceeds(t
 		_, _ = pw.Write([]byte("data: {\"type\":\"response.done\",\"response\":{\"usage\":{\"input_tokens\":2,\"output_tokens\":3,\"input_tokens_details\":{\"cached_tokens\":1}}}}\n\n"))
 	}()
 
-	result, err := svc.handleStreamingResponsePassthrough(c.Request.Context(), resp, c, &Account{ID: 1}, time.Now())
+	result, err := svc.handleStreamingResponsePassthrough(c.Request.Context(), resp, c, &Account{ID: 1}, time.Now(), "", "")
 	_ = pr.Close()
 	require.NoError(t, err)
 	require.NotNil(t, result)