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/fs/tool-fs-search/package.json

@@ -44,7 +44,7 @@
     "@deepseek-ai/dsh-agent": "workspace:^",
     "@deepseek-ai/dsh-bash": "workspace:^",
     "@deepseek-ai/dsh-bash-local": "workspace:^",
-    "@deepseek-ai/dsh-process-local": "workspace:^",
+    "@deepseek-ai/dsh-subprocess-local": "workspace:^",
     "@deepseek-ai/dsh-invariants": "workspace:^",
     "@deepseek-ai/dsh-llm": "workspace:^",
     "@deepseek-ai/dsh-retention": "workspace:^",

packages/fs/tool-fs-search/tests/integration.spec.ts

@@ -18,7 +18,7 @@ import { CallId } from '@deepseek-ai/dsh-llm'
 import SystemPrompt from '@deepseek-ai/dsh-system-prompt'
 import ToolRegistry, { TOOL_ABORTED_BEFORE_DISPATCH } from '@deepseek-ai/dsh-tools'
 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 ToolFsSearch from '@deepseek-ai/dsh-tool-fs-search'
 
 const testToolSignal = new AbortController().signal
@@ -62,7 +62,7 @@ describe.skipIf(!hasRg)('search tools over the real bash executor + real rg', ()
     ctx = new Context()
     await ctx.plugin(SystemPrompt)
     await ctx.plugin(ToolRegistry)
-    await ctx.plugin(LocalProcessManager)
+    await ctx.plugin(LocalSubprocessService)
     await ctx.plugin(LocalBashExecutor, { cwd: dir, timeoutMs: 20_000 })
     await ctx.plugin(ToolFsSearch)
   })