feat(gateway): 实现负载感知的账号调度优化

- 新增调度配置：粘性会话排队、兜底排队、负载计算、槽位清理
- 实现账号级等待队列和批量负载查询（Redis Lua 脚本）
- 三层选择策略：粘性会话优先 → 负载感知选择 → 兜底排队
- 后台定期清理过期槽位，防止资源泄漏
- 集成到所有网关处理器（Claude/Gemini/OpenAI）

backend/internal/repository/concurrency_cache_integration_test.go

@@ -27,7 +27,7 @@ type ConcurrencyCacheSuite struct {
 
 func (s *ConcurrencyCacheSuite) SetupTest() {
 	s.IntegrationRedisSuite.SetupTest()
-	s.cache = NewConcurrencyCache(s.rdb, testSlotTTLMinutes)
+	s.cache = NewConcurrencyCache(s.rdb, testSlotTTLMinutes, int(testSlotTTL.Seconds()))
 }
 
 func (s *ConcurrencyCacheSuite) TestAccountSlot_AcquireAndRelease() {
@@ -218,6 +218,48 @@ func (s *ConcurrencyCacheSuite) TestWaitQueue_DecrementNoNegative() {
 	require.GreaterOrEqual(s.T(), val, 0, "expected non-negative wait count")
 }
 
+func (s *ConcurrencyCacheSuite) TestAccountWaitQueue_IncrementAndDecrement() {
+	accountID := int64(30)
+	waitKey := fmt.Sprintf("%s%d", accountWaitKeyPrefix, accountID)
+
+	ok, err := s.cache.IncrementAccountWaitCount(s.ctx, accountID, 2)
+	require.NoError(s.T(), err, "IncrementAccountWaitCount 1")
+	require.True(s.T(), ok)
+
+	ok, err = s.cache.IncrementAccountWaitCount(s.ctx, accountID, 2)
+	require.NoError(s.T(), err, "IncrementAccountWaitCount 2")
+	require.True(s.T(), ok)
+
+	ok, err = s.cache.IncrementAccountWaitCount(s.ctx, accountID, 2)
+	require.NoError(s.T(), err, "IncrementAccountWaitCount 3")
+	require.False(s.T(), ok, "expected account wait increment over max to fail")
+
+	ttl, err := s.rdb.TTL(s.ctx, waitKey).Result()
+	require.NoError(s.T(), err, "TTL account waitKey")
+	s.AssertTTLWithin(ttl, 1*time.Second, testSlotTTL)
+
+	require.NoError(s.T(), s.cache.DecrementAccountWaitCount(s.ctx, accountID), "DecrementAccountWaitCount")
+
+	val, err := s.rdb.Get(s.ctx, waitKey).Int()
+	if !errors.Is(err, redis.Nil) {
+		require.NoError(s.T(), err, "Get waitKey")
+	}
+	require.Equal(s.T(), 1, val, "expected account wait count 1")
+}
+
+func (s *ConcurrencyCacheSuite) TestAccountWaitQueue_DecrementNoNegative() {
+	accountID := int64(301)
+	waitKey := fmt.Sprintf("%s%d", accountWaitKeyPrefix, accountID)
+
+	require.NoError(s.T(), s.cache.DecrementAccountWaitCount(s.ctx, accountID), "DecrementAccountWaitCount on non-existent key")
+
+	val, err := s.rdb.Get(s.ctx, waitKey).Int()
+	if !errors.Is(err, redis.Nil) {
+		require.NoError(s.T(), err, "Get waitKey")
+	}
+	require.GreaterOrEqual(s.T(), val, 0, "expected non-negative account wait count after decrement on empty")
+}
+
 func (s *ConcurrencyCacheSuite) TestGetAccountConcurrency_Missing() {
 	// When no slots exist, GetAccountConcurrency should return 0
 	cur, err := s.cache.GetAccountConcurrency(s.ctx, 999)