feat(queue): 增加非文本模型分布式准入队列

使用 PostgreSQL 统一同步与异步非文本任务的并发准入、持久化等待和 Worker 容量分配，并将生产 API 与独立 Worker 角色拆分。

补充策略管理、共享契约、OpenAPI、Kubernetes 双节点 Worker 清单及跨节点验收脚本；未默认启用任何生产 queue_size 策略。

已在原基线完成 Go、前端、迁移、Shell、Kustomize 与长任务容量验收；合入最新主干后将重新执行发布门禁。

apps/api/internal/runner/request_context.go

@@ -0,0 +1,47 @@
+package runner
+
+import (
+	"context"
+	"sync/atomic"
+)
+
+type submissionCancellationGate struct {
+	submitted atomic.Bool
+}
+
+type submissionCancellationGateKey struct{}
+
+func NewRequestExecutionContext(requestContext context.Context, serverContext context.Context) (context.Context, context.CancelFunc) {
+	base, cancel := context.WithCancel(context.WithoutCancel(requestContext))
+	gate := &submissionCancellationGate{}
+	ctx := context.WithValue(base, submissionCancellationGateKey{}, gate)
+	go func() {
+		select {
+		case <-serverContext.Done():
+			cancel()
+		case <-requestContext.Done():
+			if !gate.submitted.Load() {
+				cancel()
+				return
+			}
+			select {
+			case <-serverContext.Done():
+				cancel()
+			case <-base.Done():
+			}
+		case <-base.Done():
+		}
+	}()
+	return ctx, cancel
+}
+
+func markUpstreamSubmissionStarted(ctx context.Context) {
+	if gate, ok := ctx.Value(submissionCancellationGateKey{}).(*submissionCancellationGate); ok {
+		gate.submitted.Store(true)
+	}
+}
+
+func requestCancelledBeforeSubmission(ctx context.Context) bool {
+	gate, ok := ctx.Value(submissionCancellationGateKey{}).(*submissionCancellationGate)
+	return ok && ctx.Err() != nil && !gate.submitted.Load()
+}