fix(tool-tasks): claim completion notices only for the mount's own scope

Moving the task registry to the host plane put every preset's `tool-tasks`
listener on ONE `LocalTaskService`. `settle()` computes a single snapshot and
walks every registered listener with no scope filter, and it marks `reported`
only when a waiter is present — so a task settling without a waiter reached
each mount's listener with `reported` false and every one of them injected the
same completion into the same owner. Three shipped presets carry `tool-tasks`,
and a preset file edit adds a second generation of the same mount, so an agent
read N copies of one notice as model-visible durable context.

A mount now claims an owner only when the owner's scope chain reaches the
mount's own scope. An unscoped mount is the host-plane instance that serves
every agent, which keeps the TUI composition and every existing test intact.

Registry-side ownership was the alternative: mark `reported` once the first
listener claims it. It is wrong because `onTaskDone` is not a notice-only
seam — the `dsh-tasks` invariant companion registers a validating listener —
so first-claim-wins would silence observers that are not delivering anything.

The regression test mounts two scoped `tool-tasks` over one registry and
settles an unowned-wait task, which is the only path that reaches the notice
listeners at all: the shipped-composition e2e uses `wait: true`, and a waiter
marks `reported` before settlement, so that test structurally cannot cover it.

Also corrects the standing-mounts Agent Note, which still listed `tasks-local`
among the stateful PRESET plugins.

Refs #2141

packages/tasks/tool-tasks/README.zh.md

@@ -20,6 +20,8 @@
 
 一项尚未报告的完成会把 `background task <id> (<kind>: <label>) finished [status: ...]. Read its output with task_output.` 注入到确切所有者的 next-step inbox。应用上限时，即使采用 PTY 支持的 64 字节下限，稳定 id 前缀和收集命令的优先级也高于可变 label/detail，因此通知仍可操作。注入是等待后续 pre-step 领取的持久上下文，并非唤醒；取消或 owner 释放可能在领取前丢弃它。kill 或针对已终止任务的 read/wait 会把交付标为已报告，并抑制重复通知。
 
+一个宿主注册表可能承载本插件的多份挂载——每个 agent preset 一份——而注册表会把每次结算广播给全部挂载。带 scope 的挂载只向在其自身 scope 下组合出的所有者交付，因此无论挂载了多少 preset，一个 agent 每次完成都只读到一条通知；不带 scope 的挂载是宿主平面实例，向每个所有者交付。
+
 ## 配置
 
 | key | 默认值 | 含义 |