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).

tsconfig.host.json

@@ -81,8 +81,8 @@
     { "path": "./packages/llm/llm-retry" },
     { "path": "./packages/examples/agent-spine-demo" },
     { "path": "./packages/examples/cli-demo" },
-    { "path": "./packages/process/process" },
-    { "path": "./packages/process/process-local" },
+    { "path": "./packages/subprocess/subprocess" },
+    { "path": "./packages/subprocess/subprocess-local" },
     { "path": "./packages/bash/bash" },
     { "path": "./packages/pty/pty" },
     { "path": "./packages/pty/pty-local" },