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).

scripts/gen-cordis-catalog.ts

@@ -64,12 +64,12 @@ export const LINK_MAP: Record<string, string> = {
   BashExecSpec: 'bash.md',
   BashProcess: 'bash.md',
   BashRunResult: 'bash.md',
-  DshEnvironment: 'process.md',
-  ProcessHandle: 'process.md',
-  ProcessOutcome: 'process.md',
-  ProcessOutputRead: 'process.md',
-  ProcessOutputReader: 'process.md',
-  ProcessSpawnSpec: 'process.md',
+  DshEnvironment: 'subprocess.md',
+  SubprocessHandle: 'subprocess.md',
+  SubprocessOutcome: 'subprocess.md',
+  SubprocessOutputRead: 'subprocess.md',
+  SubprocessOutputReader: 'subprocess.md',
+  SubprocessSpawnSpec: 'subprocess.md',
   CodeRunRequest: 'code-runtime.md',
   CodeRunResult: 'code-runtime.md',
   CompactionResult: 'compaction.md',