refactor(subprocess): the dispose ladder moves to its one consumer

SubprocessHandle loses dispose(graces) and SubprocessDisposeGraces: the
stdin-EOF→SIGTERM→SIGKILL sequence is teardown POLICY encoding one
consumer's cooperation shape, not process vocabulary — the seam keeps
kill/terminate/waitForExit, and waitForExit(signal?) is the quiescence
probe a consumer ladder needs. dsh-subagent-acp owns disposeAcpChild()
over those public verbs (tier tests move into its suite; a never-exits
stub pins the fail-loud path); dsh-subprocess-local sheds the ladder,
its deadline import, and the dsh-timeout dependency. Every future
backend now owes four verbs and no teardown policy. New bilingual
ladder-ownership Agent Note records the decision; catalogs regenerated.

docs/core-data-structures/subprocess.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-subprocess.md: cdd4507c7d37f47ca243ddf38114f5aa6b6f3ad1
-subprocess.zh.md: 78325c3255c42ed591bbd98fdbdb4fdfcba48202
+subprocess.md: 810f74b6512c846e138670aa6c3ad1c8be577366
+subprocess.zh.md: 8e6aca436a2a7a14ec4ab1da9b9d4f848918a9dc