fix(routing): 将 admission 排队计入平台负载

候选路由此前只统计 River 队列和历史尝试，未统计尚未生成 River Job 的异步 admission 等待任务，突发提交会集中绑定同一高优先级平台，导致其他平台容量闲置。\n\n将等待中的 gateway_task_admissions 纳入平台模型排队负载，并通过 task_id 去重保留原有统计语义，使候选路由可以在集群 admission 阶段按并发利用率分流。\n\n验证：\n- go test ./internal/store ./internal/runner -count=1\n- go vet ./internal/store ./internal/runner\n- gofmt -l internal/store/candidates.go

apps/api/internal/store/candidates.go

@@ -104,9 +104,17 @@ LEFT JOIN (
 	    AND expires_at > statement_timestamp()
 	  GROUP BY scope_key
 	) con ON con.scope_key = $5::text || m.id::text
-LEFT JOIN (
+	LEFT JOIN (
 	  SELECT queued_sources.platform_model_id, COUNT(DISTINCT queued_sources.task_id) AS waiting
 	  FROM (
+	    SELECT admission.task_id::text AS task_id,
+	           admission.platform_model_id::text AS platform_model_id
+	    FROM gateway_task_admissions admission
+	    JOIN gateway_tasks admission_task ON admission_task.id = admission.task_id
+	    WHERE admission.status = 'waiting'
+	      AND admission_task.status = 'queued'
+	      AND admission_task.next_run_at <= now()
+	    UNION ALL
 	    SELECT t.id::text AS task_id, qm.id::text AS platform_model_id
 	    FROM gateway_tasks t
 	    JOIN integration_platforms qp ON TRUE