fix(spec): scope the at-rest stored-pass clause to this shape, not to protocol 18

`conversionIds` on step 18 is NOT empty — it carries the major's other D2
conversions — so "nothing to rewrite here" could be read as "the stored pass
rewrites nothing at protocol 18", which is false. The true scope is this entry's
disposition, which adds no D2 conversion of its own (its id is 0x in
`conversions/registry.ts`, control `action-execute-to-target` lit at 1x).

`registry.ts` follows by `gen:migration-registry`.

Claude-Session: https://claude.ai/code/session_01MkQhmuuJAVDjmeWNixwDDH
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/spec/src/migrations/entries/semantic/18.element-data-source-and-object-block-filter-rule-array.ts

@@ -60,8 +60,8 @@ export const entry: SemanticMigration = {
     + '⚠️ Metadata AT REST is deliberately NOT rewritten, and this disposition adds no D2 '
     + 'conversion — a SemanticMigration converts nothing by its own type, and '
     + '`os migrate meta --stored` (the pass over a deployment\'s `sys_metadata` rows) replays '
-    + 'D2 conversions only, so it has nothing to rewrite here. The read path does not '
-    + 're-validate stored rows '
+    + 'D2 conversions only, so it has nothing to rewrite for this shape. The read path '
+    + 'does not re-validate stored rows '
     + '(`applyConversionsToStoredItem` replays the full chain without validating, by its own '
     + 'contract), so a stored page or block carrying the record form keeps loading unchanged '
     + 'and is still rendered by objectui at the pinned `.objectui-sha`; what changes is that '

packages/spec/src/migrations/registry.ts

@@ -6951,8 +6951,8 @@ const step18: MigrationStep = {
         + '⚠️ Metadata AT REST is deliberately NOT rewritten, and this disposition adds no D2 '
         + 'conversion — a SemanticMigration converts nothing by its own type, and '
         + '`os migrate meta --stored` (the pass over a deployment\'s `sys_metadata` rows) replays '
-        + 'D2 conversions only, so it has nothing to rewrite here. The read path does not '
-        + 're-validate stored rows '
+        + 'D2 conversions only, so it has nothing to rewrite for this shape. The read path '
+        + 'does not re-validate stored rows '
         + '(`applyConversionsToStoredItem` replays the full chain without validating, by its own '
         + 'contract), so a stored page or block carrying the record form keeps loading unchanged '
         + 'and is still rendered by objectui at the pinned `.objectui-sha`; what changes is that '