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/README.zh.md

@@ -9,7 +9,7 @@
 | `agent-presets/` | preset 词汇、在受信任目录与用户自建目录上的文件系统发现，以及带校验的按 agent 挂载 | `ctx.agentPresets` |
 | `persona/` | 把 agent 人设做成可组装的行，使 preset 不止能改工具、也能改身份 | — |
 
-部署随附三个 preset：`standard`（完整编码 agent）、`core-web`（两个工具的 benchmark 表层），以及 `cordis`（标准 agent 加上自指工具集与一份组装创作 skill，使人可以让 agent 去创作另一个 agent）。
+部署随附三个 preset：`standard`（完整编码 agent）、`minimal`（两个工具的 benchmark 表层），以及 `cordis`（标准 agent 加上自指工具集与一份组装创作 skill，使人可以让 agent 去创作另一个 agent）。
 
 本组假定的组装划分是：注册表与跨会话设施是进程单例，留在宿主组装中；preset 只承载单个 agent 对它们的贡献。若 preset 中某一行发布了进程级全局服务，挂载时即被拒绝，而不是留到与下一个会话相撞。