feat(agent-presets): rename the two-tool preset to minimal

`core-web` said neither of the things that matter about it. The `-web`
suffix is a leftover from the whole-process `core-web.cordis.yml` overlay,
and presets are per-session and not web-specific. `core` reads as "the
foundational one" when it is in fact the one with the fewest capabilities.

`minimal` says what it is and orders the shipped set legibly by capability:
minimal, standard, cordis.

Breaking: a session created under `core-web` records that id in its header
and will fail to resolve it on resume. Nothing outside this repository has
shipped, so no migration path is offered.

The identically named `config/core-web.cordis.yml` — the legacy
whole-process overlay behind the web snapshot test — is a different thing
and keeps its name.

packages/preset/agent-presets/README.md

@@ -82,7 +82,7 @@ When a settings provider is composed, this plugin registers the `agent-presets`
 
 ```yaml
 agent-presets:
-  default: core-web
+  default: minimal
 ```
 
 The value is read per resolution rather than snapshotted, so a hot-reloaded document takes effect on the next session created and every running session stays on the preset it was composed from. Clearing the user field re-inherits the composition default. A default naming a preset no root supplies is stored without complaint and fails at the next `resolve()` — the roster is a live directory, so a name absent now may exist by the time a session asks for it.

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

@@ -82,7 +82,7 @@ description: 只向模型呈现 bash 与 str_replace_editor，适合 benchmark
 
 ```yaml
 agent-presets:
-  default: core-web
+  default: minimal
 ```
 
 该值在每次解析时读取而非快照，因此热重载的文档对**此后创建**的会话生效，而每个运行中的会话仍停留在它当初据以组装的 preset 上。清空用户字段即重新继承组装默认值。若默认值指向没有任何根目录提供的 preset，写入时不会报错，而在下一次 `resolve()` 时失败——名单是一个活动目录，此刻不存在的名字，等到某个会话真正索取时可能已经存在。