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).

vitest.config.ts

@@ -11,7 +11,7 @@ const windowsUnsupportedPackages = process.platform === 'win32'
   ? [
       'packages/bash/*',
       'packages/hooks/*',
-      'packages/process/*',
+      'packages/subprocess/*',
       'packages/pty/pty-local',
       'packages/sandbox/sandbox-local',
       'packages/sdk/create-sdk',
@@ -41,7 +41,7 @@ const testIncludes = [
 // that worker threads cannot isolate reliably under aggregate gate contention.
 // Keep the narrow exception in forks while the rest of the inventory avoids per-file processes.
 const processBoundTests = [
-  'packages/process/process-local/tests/spawn.spec.ts',
+  'packages/subprocess/subprocess-local/tests/spawn.spec.ts',
   'packages/context/time-context/tests/time-context.spec.ts',
   'packages/llm/llm-pi-ai/tests/adapter.spec.ts',
   'packages/ui/app-boot/tests/app-boot.spec.ts',