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).

examples/headless-agent/tests/code-mode.e2e.ts

@@ -13,7 +13,7 @@ import AgentRegistry, { type Agent } from '@deepseek-ai/dsh-agent'
 
 import AgentLoop from '@deepseek-ai/dsh-agent-loop'
 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 * as ToolBash from '@deepseek-ai/dsh-tool-bash'
 import * as LlmDeepSeek from '@deepseek-ai/dsh-llm-deepseek'
 import { WorkerCodeRuntime } from '@deepseek-ai/dsh-code-runtime-worker'
@@ -56,7 +56,7 @@ async function codeModeHarness(cwd: string): Promise<Context> {
   await harness.plugin(AgentRegistry)
   await harness.plugin(AgentLoop, { agents: [] })
   await harness.plugin(LlmDeepSeek)
-  await harness.plugin(LocalProcessManager)
+  await harness.plugin(LocalSubprocessService)
   await harness.plugin(LocalBashExecutor, { cwd, timeoutMs: 30_000 })
   await harness.plugin(ToolBash)
   await harness.plugin(WorkerCodeRuntime, {})
@@ -116,7 +116,7 @@ async function backgroundCodeModeHarness(cwd: string): Promise<Context> {
   const harness = await typedCodeModeHarness()
   await harness.plugin(LocalTaskService)
   await harness.plugin(ToolTasks, {})
-  await harness.plugin(LocalProcessManager)
+  await harness.plugin(LocalSubprocessService)
   await harness.plugin(LocalBashExecutor, { cwd, timeoutMs: 30_000 })
   await harness.plugin(ToolBash)
   return harness