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/examples/agent-spine-demo/package.json

@@ -65,7 +65,7 @@
     "@deepseek-ai/dsh-llm": "workspace:^",
     "@deepseek-ai/dsh-paths": "workspace:^",
     "@deepseek-ai/dsh-llm-retry": "workspace:^",
-    "@deepseek-ai/dsh-process-local": "workspace:^",
+    "@deepseek-ai/dsh-subprocess-local": "workspace:^",
     "@deepseek-ai/dsh-sandbox-local": "workspace:^",
     "@deepseek-ai/dsh-sandbox-policy": "workspace:^",
     "@deepseek-ai/dsh-scope": "workspace:^",

packages/examples/agent-spine-demo/tests/multi-project-sandbox.e2e.ts

@@ -5,7 +5,7 @@ import { basename, join } from 'node:path'
 import { afterEach, beforeEach, describe, expect, it } from 'vitest'
 import { Context } from 'cordis'
 import { SandboxBashExecutor } from '@deepseek-ai/dsh-bash-sandbox'
-import LocalProcessManager from '@deepseek-ai/dsh-process-local'
+import LocalSubprocessService from '@deepseek-ai/dsh-subprocess-local'
 import * as FsPolicy from '@deepseek-ai/dsh-fs-policy'
 import SandboxedFileSystem from '@deepseek-ai/dsh-fs-sandbox'
 import { CallId } from '@deepseek-ai/dsh-llm'
@@ -53,7 +53,7 @@ beforeEach(async () => {
   ctx = new Context()
   await ctx.plugin(LocalSandboxProvider, {})
   await ctx.plugin(SandboxPolicyService, { mode: 'workspace-write', workspaceRoot: fallbackRoot })
-  await ctx.plugin(LocalProcessManager)
+  await ctx.plugin(LocalSubprocessService)
   await ctx.plugin(SandboxBashExecutor, { cwd: fallbackRoot, timeoutMs: 30_000 })
   await ctx.plugin(SandboxedFileSystem, { cwd: fallbackRoot })
   await ctx.plugin(agentSpine, {