重构 worker 对话：复用 resume 机制，改专属 goroutine 运行

把「给运行中 Worker 发消息调方向」从自建的介入持久化协议，改为复用
已有的暂停/恢复 + transcript resume 能力，实现与主 Agent chat 一致。

- 拆 runWorkerStep：抽出 runIntent(执行+善后)，池子与消息路径共用一份
  善后逻辑；新增 runDetachedIntent，把意图 paused→running(不经 frontier)
  并在专属 goroutine 里直接跑，用户消息不受 3 槽池限制、随发随跑。
- 精简 sendWorkerMessage handler：校验 + emit 用户活动 + 专属运行；消息经
  ExecuteWithMessage 作为下一轮输入注入，request_id 仅做 transcript 去重。
- 删除介入 DB 协议与 15 处 activity 查询过滤(回退 exploration.go)、
  directedClaims 调度屏障、RecoverWorkerMessages 恢复、workerWake/waitWorker、
  AbortWorkIntervenedByUser。无 DB schema 改动。
- 前端：保留消息框，恢复「直接继续」(resume)按钮；发送改由 SSE 承载，
  去掉乐观插入。
- 取舍(低频可接受)：消息仅存内存，不做崩溃恢复；发消息时该任务可能瞬时
  超并发 1 个 worker。

净改动 9 文件 +583/-46(原 PR 15 文件 +1940/-72)。

server/manager.go

@@ -63,7 +63,6 @@ type Task struct {
 	Store                *pgdb.ExplorationStore `json:"-"`
 	Guard                *guard.Guard           `json:"-"`
 	notify               chan struct{}
-	workerWake           chan struct{}
 	lifecycleMu          sync.RWMutex
 	llmMu                sync.RWMutex
 
@@ -738,7 +737,7 @@ func taskFromPG(pt *pgdb.Task, store *pgdb.ExplorationStore, ic *intercept.Inter
 		TimeoutSeconds: pt.TimeoutSeconds, PlanHeartbeatSeconds: pt.PlanHeartbeatSeconds,
 		CoverageEnabled: pt.CoverageEnabled,
 		FirstRunAt:      unixOrZero(pt.FirstRunAt), DeadlineAt: unixOrZero(pt.DeadlineAt),
-		Store: store, Guard: guard.NewWithInterceptor(ic), notify: make(chan struct{}, 1), workerWake: make(chan struct{}, 64),
+		Store: store, Guard: guard.NewWithInterceptor(ic), notify: make(chan struct{}, 1),
 	}
 }
 
@@ -1639,20 +1638,6 @@ func (t *Task) Notify() {
 	}
 }
 
-// NotifyWorker wakes one idle execution slot without also scheduling a Planner
-// round. The channel is separate from notify because human intervention needs
-// the reopened intent reclaimed immediately, while graph-change notifications
-// are Planner-facing and debounced. A nil channel is tolerated by test fixtures.
-func (t *Task) NotifyWorker() {
-	if t == nil || t.workerWake == nil {
-		return
-	}
-	select {
-	case t.workerWake <- struct{}{}:
-	default:
-	}
-}
-
 // NotifyDone is Notify plus a hint: a worker just finished intentID and that is
 // what triggered this wake-up. The planner reads the accumulated triggers next
 // round so it can spell out which intent finished (+ its output). Events pile up