refactor(tasks): 后台任务改读宿主客户端 jobs 服务，删除自建三条路由

- 新增 src/client/jobs-client.ts：结构探测 ctx.jobs（watchRows / observe /
  state / kill），引用计数的按会话 roster 订阅、只观测展开的那一行、
  跨树去重（无主任务归到承载它的被观测会话，树外 owner 丢弃）。
- 抽屉与输出浮窗改读该服务：行来自推送 roster（状态 / 时长 / owner / 进度），
  输出面换 TerminalBlock 显示宿主为观察者流的保留输出（gapBefore → 截断提示、
  error → 失败提示），kill 走 jobs.kill(owner, jobId)，两击确认不变。
- 自动激活（use-host-feeds）改骑同一条推送 roster；detectNewJob 增加
  「观测起点时钟」参数，避免「页面打开时已在跑的任务」被当成新工作。
- 删除 src/jobs-routes.ts（+ tests/jobs-routes.spec.ts）、index.ts 的三条路由、
  api.jobsList/jobOutput/jobKill 与 JobOutputResult、context-types 的
  SidebarJobsService（换成 SidebarClientJobsService/SidebarJobsSnapshot/
  SidebarObservedJob 镜像，SidebarJobView 补 owner/progress）、
  页面里的 jobs.list 轮询与 collectTreeJobs。
- 三个 spec 改用假 ctx.jobs 服务（jobs-view 14 例 / 自动激活 12 例 /
  页面 20 例）：观测只在展开行、切换与关闭释放观测、watch 隐藏时不建立、
  卸载时全部释放、无服务时不渲染任务面。

验证：typecheck / lint 通过；pnpm test 1240 passed / 9 skipped；pnpm build + pack 通过。

(cherry picked from commit 7d9b82e73190218f05910433ed520cb90e4d4ab2)

src/client/api.ts

@@ -11,7 +11,6 @@ import type { SidechatLiveEvent, SidechatLogEvent, SidechatThreadInfo } from '..
 import type {
   SidebarCreateTeamTaskRequest,
   SidebarChildLiveView,
-  SidebarJobView,
   SidebarSessionEvent,
   SidebarTeamMemberView,
   SidebarTeamTaskMutationResult,
@@ -104,21 +103,6 @@ export interface FsTextResult { kind: 'text'; content: string; truncated: boolea
  *  `head` carries the first bytes (base64) for viewer detect sniffing. */
 export interface FsBinaryResult { kind: 'binary'; size: number; truncated: boolean; head: string }
 
-/**
- * One jobs.output response: the output the MODEL has read so far for the
- * job (replayed from the owner session's event log — the model's
- * job_output cursor is never touched, so the pane can never steal the
- * agent's bytes). `read` is false until the model actually called
- * job_output for the job.
- */
-export interface JobOutputResult {
-  text: string
-  /** True when the host capped the text at its output limit. */
-  truncated: boolean
-  /** Whether the model has read the job at least once. */
-  read: boolean
-}
-
 /** The `subagents.live` response: one row per tree child (and the root). */
 export type SubagentLiveResult = { live: Record<string, SidebarChildLiveView> }
 
@@ -348,30 +332,6 @@ export const api = {
   /** Cherry-pick one commit onto the current branch. */
   gitCherryPick: (scope: SessionScope, hash: string, worktree?: string) =>
     call<{ ok: true }>('git.cherry-pick', gitPayload(scope, worktree, { hash })),
-  /**
-   * The output the model has read so far for one background job (replayed
-   * from the owner session's event log — never the model's job_output
-   * cursor). The scope MUST be the job's OWNER session.
-   */
-  jobOutput: (scope: SessionScope, id: string, signal?: AbortSignal) =>
-    call<JobOutputResult>('jobs.output', scopePayload(scope, { id }), signal),
-  /**
-   * The background-job list of one session (the Tasks page's jobs section and
-   * the job auto-open trigger). DSH 0.1.7 dropped the client session
-   * snapshot's jobs mirror, so the registry is read through the plugin's own
-   * `jobs.list` route. The registry's access fence admits a job to its OWNER
-   * session (and to unowned jobs) only, so a caller that needs the whole tree
-   * asks once per tree session. A host without the jobs service answers 503:
-   * the rejection is the caller's to degrade from (an empty section).
-   */
-  jobsList: (sessionId: string, signal?: AbortSignal) =>
-    call<{ jobs: SidebarJobView[] }>('jobs.list', { sessionId }, signal),
-  /** Request cancellation of one background job (live jobs flip to stopping). */
-  jobKill: (scope: SessionScope, id: string, reason?: string) =>
-    call<{ ok: true; outcome: 'requested' | 'already-finished' }>('jobs.kill', scopePayload(scope, {
-      id,
-      ...(reason !== undefined ? { reason } : {}),
-    })),
   /**
    * One batch live-preview fetch for the whole Subagent tree. The payload is
    * the already-resolved topology ROOT (not a session scope); the host