feat(app-boot): register cordis:group beside cordis:include

A composition that shares one `isolate` realm across rows needs a
`cordis:group` row, and a preset living outside this workspace — the
authored ones under the Harness home — cannot resolve
`@cordisjs/plugin-group` by name: Node's upward `node_modules` walk
never reaches the harness from there. Registering it as a loader builtin
beside `cordis:include` loads both through the ambient module pipeline
instead.

Record it in the preset Agent Note, which leans on the realm vocabulary
without saying where the group row comes from, and drop the preset
README's limitation claiming this builtin is unavailable — it described
the state this change ends.

The test's assertion had a vacuous escape: `provide` mints the root
symbol unconditionally, so the `rootKey === undefined` disjunct could
never hold and the comment claiming the root realm never learned the
name was wrong. Pin both halves — the symbol exists, nothing is stored
under it — and clean up the global the fixture writes.

packages/preset/agent-presets/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/preset/agent-presets/README.md
-README.md: 5d66c23f24717d1c30a9e729c7b0528715692d41
-README.zh.md: 9cdcd8b11a8a37d6d789c393e9a1500e4fbfd503
+README.md: e53a52f145b3f66ab115b93c614561fed8194719
+README.zh.md: 39b470002816f309c8ec9af1d72e04495b020ad7

packages/preset/agent-presets/README.md

@@ -58,5 +58,4 @@ Prefix-stable for the life of an agent: a composition is installed once, before
 
 - **A preset cannot be changed on a live agent** — the mount happens once during creation, so switching a running session's composition would mean unwinding its subtree mid-turn, dropping tools the model may already have called. Changing the default affects only sessions created afterwards.
 - **Display names are the directory id** — a preset carries no manifest, so pickers and settings surfaces show the id until a consumer needs richer metadata.
-- **`isolate` realms cannot be expressed across rows without `cordis:group`** — an entry-local realm works on a single row, but grouping a provider with its consumers under one shared realm needs the group builtin, which `dsh-app-boot` does not register.
 - **Root scans are not watched** — every read hits the filesystem instead, which keeps the roster fresh but puts one `readdir` per root on each `list()`.

packages/preset/agent-presets/README.zh.md

@@ -58,5 +58,4 @@ Indirectly, through the plugins a mounted composition registers, which own every
 
 - **无法在存活的 agent 上更换 preset** —— 挂载只在创建时发生一次，因此切换运行中会话的组装意味着要在轮次进行途中卸载其子树，抽走模型可能已经调用的工具。更改默认值只影响此后创建的会话。
 - **展示名称就是目录 id** —— preset 不携带 manifest，因此选择器与设置界面在有消费方需要更丰富的元数据之前，只显示 id。
-- **跨多行的 `isolate` realm 需要 `cordis:group` 才能表达** —— 单行可用 entry 本地 realm，但要把一个提供方与它的消费方归入同一个共享 realm，需要 group 内建插件，而 `dsh-app-boot` 并未注册它。
 - **根目录扫描不做监听** —— 每次读取都实际访问文件系统，这让名单保持新鲜，但每次 `list()` 会对每个根目录产生一次 `readdir`。