refactor(subprocess): rename the process seam to subprocess and address review

Review feedback (tianyicui): 'process' is a poor service name. The family is
now packages/subprocess/ — @deepseek-ai/dsh-subprocess (ctx.subprocess,
abstract SubprocessService, Subprocess* vocabulary) and
@deepseek-ai/dsh-subprocess-local (LocalSubprocessService) — renamed
throughout code, compositions, docs (en+zh, pairs re-recorded), catalogs,
and gates. 'subprocess' is the precise term for managed OS children (the
Python-stdlib sense), avoids colliding with Node's global process object,
and reads as one system beside dsh-subagent-subprocess.

ds-review-bot findings addressed:
- kill() on a settled handle is now a no-op (no signal to a possibly-reused
  pgid, no referenced grace timer delaying exit); pinned by a spy test.
- The moved DshEnvironmentKey/DshEnvironment/CollectedOutput types get
  drift-checked type-equiv blocks on the new subprocess.md page, restoring
  their manifest registration.
- subprocess.md is registered in the core.md sub-page index (en+zh).

docs/core-data-structures/core.zh.md

@@ -31,6 +31,7 @@ harness 是一个微内核：一个极小的核心加上众多插件。大多数
 | [user-interaction.md](user-interaction.md) | UI 支持的人工问答 seam：`AskUserQuestionRequest`、answer/options 词汇、提供方 API、错误分类体系 |
 | [approval.md](approval.md) | 一次性用户审批 seam：`ApprovalRequest`、`ApprovalOutcome`、逐会话策略、审计与 answerer 契约 |
 | [bash.md](bash.md) | bash 执行器 seam：`BashExecRequest`/`Spec`、`BashRunResult`、后台 `BashProcess` 句柄 |
+| [subprocess.md](subprocess.md) | 子进程 seam：完全显式的 `SubprocessSpawnSpec`、基于偏移的输出读取器、不含分类的 `SubprocessOutcome`，以及受管 `DSH_*` 环境词汇 |
 | [pty.md](pty.md) | 持久化终端 ID、后端/会话契约、发送就绪状态、有界读取与 owner 可见快照 |
 | [sandbox.md](sandbox.md) | 每会话策略解析与进程约束 seam：文件效果模式、执行/提供方策略、`ConfinedArgv`、强制执行与故障关闭错误 |
 | [code-runtime.md](code-runtime.md) | 代码执行 seam：`CodeRunRequest`/`Result`、绑定命名空间、捕获日志、`CodeRunFailure` 分类体系 |