chore(changeset): patch for the stage-11 rationale and comment rewrite

The step rationales ship in @objectstack/spec's dist (dist/migrations/index.js
and .mjs carry the new phrases, the old ones in 0 files, an unchanged control
phrase in the same 2), so the release takes a patch note. Clause-②: no.

Claude-Session: https://claude.ai/code/session_01YDt3PzwfrkuFzUBF89WPmM
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/spec-migration-registry-rationale-decisions-in-words.md

@@ -0,0 +1,19 @@
+---
+'@objectstack/spec': patch
+---
+
+Nine migration-step rationale passages state their decisions in words instead of tracker numbers, and two registry comments cite the commit that decided them
+
+Clause-②: no
+
+The protocol 17 and protocol 18 step rationales are what `os migrate meta` shows per hop
+and what the protocol upgrade guide prints. Nine of their passages named GitHub issues
+that no longer exist, so an upgrading author met a number with nothing behind it. Each of
+those passages now carries no number at all and says what was decided: why `mongo` and
+`mongodb` are both accepted, why the form-view option `default` and `connector.errorMapping`
+were retired, which earlier cleanup the import mapping `lookup` params finish, what the
+memory driver's placeholder refusal extends, how the plugin manifest's `contributes`
+members and `routes` were retired, and why the stack `themes` carrier and the
+component-translation `submitLabel` key went. Two source comments of the migration
+registry now cite the commit behind them. Text only: no migration step, entry, retired key
+or def, conversion, schema, export or runtime behaviour changes.