feat(worker): 实现集群限流与自适应负载

保留平台模型 RPM、TPM 和并发策略语义，增加 PostgreSQL 集群级租约、饱和候选重选和多平台自动负载，避免突发任务固定等待首个平台。\n\n新增 Worker 实时负载采样、自适应 active/heavy 容量、心跳与管理端指标，并扩展本地 acceptance runner，覆盖三 Worker、同模型三平台 2/4/6 并发和 48 个带图视频突发任务。\n\n验证：go test ./...、go vet ./...、PostgreSQL 跨 Store 集成测试、gofmt、bash -n、ShellCheck 及本地集群 provider-burst 验收通过；48/48 成功，无越限、重复提交、重复计费、重复回调或终态资源泄漏。

apps/api/internal/store/rate_limits.go

@@ -184,12 +184,12 @@ func reserveConcurrencyLease(ctx context.Context, tx pgx.Tx, taskID string, atte
 	var nextAvailableAt time.Time
 	if err := tx.QueryRow(ctx, `
 SELECT COALESCE(SUM(lease_value), 0)::float8,
-       COALESCE(MIN(expires_at), now() + ($3::int * interval '1 second'))
+       COALESCE(MIN(expires_at), statement_timestamp() + ($3::int * interval '1 second'))
 FROM gateway_concurrency_leases
 WHERE scope_type = $1
   AND scope_key = $2
   AND released_at IS NULL
-  AND expires_at > now()`,
+  AND expires_at > statement_timestamp()`,
 		reservation.ScopeType,
 		reservation.ScopeKey,
 		reservation.LeaseTTLSeconds,
@@ -218,14 +218,20 @@ WHERE scope_type = $1
 	}
 	var leaseID string
 	if err := tx.QueryRow(ctx, `
-INSERT INTO gateway_concurrency_leases (task_id, attempt_id, scope_type, scope_key, lease_value, expires_at)
-VALUES ($1::uuid, NULLIF($2, '')::uuid, $3, $4, $5, now() + ($6::int * interval '1 second'))
+INSERT INTO gateway_concurrency_leases (
+  task_id, attempt_id, scope_type, scope_key, lease_value, limit_value, acquired_at, expires_at
+)
+VALUES (
+  $1::uuid, NULLIF($2, '')::uuid, $3, $4, $5, $6,
+  statement_timestamp(), statement_timestamp() + ($7::int * interval '1 second')
+)
 RETURNING id::text`,
 		taskID,
 		attemptID,
 		reservation.ScopeType,
 		reservation.ScopeKey,
 		reservation.Amount,
+		reservation.Limit,
 		reservation.LeaseTTLSeconds,
 	).Scan(&leaseID); err != nil {
 		return ConcurrencyLease{}, err
@@ -381,7 +387,7 @@ func (s *Store) ReleaseConcurrencyLeases(ctx context.Context, leases []Concurren
 	}
 	if _, err := tx.Exec(ctx, `
 UPDATE gateway_concurrency_leases
-SET released_at = now()
+SET released_at = statement_timestamp()
 WHERE id = ANY($1::uuid[]) AND released_at IS NULL`, leaseIDs); err != nil {
 		return err
 	}
@@ -411,7 +417,7 @@ func (s *Store) RenewConcurrencyLeases(ctx context.Context, leases []Concurrency
 	}
 	tag, err := s.pool.Exec(ctx, `
 UPDATE gateway_concurrency_leases lease
-SET expires_at = now() + (renewal.ttl_seconds * interval '1 second')
+SET expires_at = statement_timestamp() + (renewal.ttl_seconds * interval '1 second')
 FROM unnest($1::uuid[], $2::int[]) AS renewal(id, ttl_seconds)
 WHERE lease.id = renewal.id
   AND lease.released_at IS NULL
@@ -705,7 +711,7 @@ WHERE attempt.task_id = task.id
 	result.FailedAttempts = tag.RowsAffected()
 	tag, err = tx.Exec(ctx, `
 UPDATE gateway_concurrency_leases
-SET released_at = now()
+SET released_at = statement_timestamp()
 WHERE task_id = ANY($1::uuid[])
   AND released_at IS NULL`, taskIDs)
 	if err != nil {
@@ -772,7 +778,7 @@ FOR UPDATE OF task SKIP LOCKED`, runtimeRecoveryBatchSize)
 	var result RuntimeRecoveryResult
 	tag, err := tx.Exec(ctx, `
 UPDATE gateway_concurrency_leases
-SET released_at = now()
+SET released_at = statement_timestamp()
 WHERE task_id = ANY($1::uuid[])
   AND released_at IS NULL`, taskIDs)
 	if err != nil {