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).

scripts/gen-tool-catalog.ts

@@ -19,7 +19,7 @@ import ToolRegistry, { type Config as ToolsConfig } from '@deepseek-ai/dsh-tools
 import { BashExecutor } from '@deepseek-ai/dsh-bash'
 import type { BashExecRequest, BashExecSpec, BashProcess, BashRunResult } from '@deepseek-ai/dsh-bash'
 import LocalBashExecutor from '@deepseek-ai/dsh-bash-local'
-import LocalProcessManager from '@deepseek-ai/dsh-process-local'
+import LocalSubprocessService from '@deepseek-ai/dsh-subprocess-local'
 import LocalFileSystem from '@deepseek-ai/dsh-fs-local'
 import UserInteractionService from '@deepseek-ai/dsh-user-interaction'
 import PlanModeService from '@deepseek-ai/dsh-plan-mode'
@@ -198,7 +198,7 @@ const TOOL_PACKAGES: ToolPackage[] = [
     requires: ['ctx.tools', 'ctx.bash', 'ctx.tasks at call time for run_in_background'],
     writes: ['tool/call', 'tool/result'],
     async mount(ctx) {
-      await ctx.plugin(LocalProcessManager)
+      await ctx.plugin(LocalSubprocessService)
       await ctx.plugin(LocalBashExecutor)
       await ctx.plugin(ToolBash)
     },