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).

packages/bash/bash-sandbox/tests/bwrap.e2e.ts

@@ -9,7 +9,7 @@ import { LocalSandboxProvider } from '@deepseek-ai/dsh-sandbox-local'
 import { SandboxPolicyService } from '@deepseek-ai/dsh-sandbox-policy'
 import { bwrapProfileArgs } from '@deepseek-ai/dsh-sandbox-local/src/profiles.ts'
 import { SandboxBashExecutor } from '@deepseek-ai/dsh-bash-sandbox'
-import LocalProcessManager from '@deepseek-ai/dsh-process-local'
+import LocalSubprocessService from '@deepseek-ai/dsh-subprocess-local'
 
 /**
  * Keyless integration of the real provider and executor through public run/start paths. With
@@ -43,7 +43,7 @@ async function sandboxedBash(workspace: string, mode: 'read-only' | 'workspace-w
   ctx = new Context()
   await ctx.plugin(LocalSandboxProvider, {})
   await ctx.plugin(SandboxPolicyService, { mode, workspaceRoot: workspace })
-  await ctx.plugin(LocalProcessManager)
+  await ctx.plugin(LocalSubprocessService)
   await ctx.plugin(SandboxBashExecutor, { cwd: workspace, timeoutMs: 30_000 })
   return ctx.bash as SandboxBashExecutor
 }