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/sdk/helper/src/features/builtin/index.ts

@@ -33,7 +33,7 @@ export function createBuiltinRegistry(profile: ProjectProfile): FeatureRegistry
       mode: 'exclusive',
       required: true,
       baseResources: [
-        { kind: 'npm-cordis-config-entry', id: 'processes', package: '@deepseek-ai/dsh-process-local' },
+        { kind: 'npm-cordis-config-entry', id: 'subprocess', package: '@deepseek-ai/dsh-subprocess-local' },
         { kind: 'npm-cordis-config-entry', id: 'tool-bash', package: '@deepseek-ai/dsh-tool-bash' },
       ],
       options: [