fix(ship): name the /document-release subagent at every Step 18 decision point

The v1.54.0.0 carve moved Step 18 (documentation sync) into
ship/sections/pr-body.md and the Claude-host skeleton stopped saying
"document-release" anywhere in the workflow body — the dispatch became
invisible at exactly the moments an agent decides whether to open the
section. Restore visibility at three touchpoints, all subagent-framed
(never bare-slash-framed, which would invite an inline Skill invocation
that bypasses the fresh-context subagent + JSON contract):

- manifest trigger (renders into the section-index row AND the STOP
  pointer): "dispatching the /document-release subagent to sync docs
  (Step 18) and then creating or updating the PR/MR (Step 19)"
- Step 17 handoff line names Step 18's dispatch explicitly
- new hoisted doc-sync invariant beside the PR-title invariant: the
  dispatch itself is never skipped; only a failed subagent is
  non-blocking

Pin it in carve-guards: 'the /document-release subagent' (all three
touchpoints) + 'dispatches the /document-release subagent' (invariant)
must stay in the skeleton; the carved imperative 'Dispatch
/document-release as a subagent' must stay carved. Skeleton cap
91,600 → 92,300 (measured 91,764; trigger renders twice). Goldens
regenerated for all three hosts.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ship/sections/manifest.json

@@ -56,7 +56,7 @@
       "id": "pr-body",
       "file": "pr-body.md",
       "title": "Documentation sync + PR/MR creation",
-      "trigger": "syncing docs and creating or updating the PR/MR (Steps 18-19)"
+      "trigger": "dispatching the /document-release subagent to sync docs (Step 18) and then creating or updating the PR/MR (Step 19)"
     }
   ]
 }