chore(spec): the dataset field narrowing takes the next free orders after the base merge

STEP18_RATIONALE fragment 57 -> 58 (57 is allocated to the in-flight
ui-record-line-items-props-closed); MAJOR_18_CONVERSIONS entry 53 -> 54 (main
landed form-field-public-picker at 53). Neither list requires unique orders.

Co-authored-by: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UtnxvdiN376GF3sgXwAw4d

Author: claude

packages/spec/src/conversions/registry.ts

@@ -13685,7 +13685,7 @@ const MAJOR_18_CONVERSIONS: readonly OrderedConversion[] = [
   { conversion: currencyConfigPrecisionRemoved, order: 41 },
   { conversion: dashboardRefreshIntervalToRefreshIntervalSeconds, order: 24 },
   { conversion: dashboardWidgetChartConfigStructureRemoved, order: 33 },
-  { conversion: datasetCountMeasureEmptyFieldRemoved, order: 53 },
+  { conversion: datasetCountMeasureEmptyFieldRemoved, order: 54 },
   { conversion: elementFilterRemoved, order: 4 },
   { conversion: elementFormRemoved, order: 5 },
   { conversion: elementInputTargetVariableRemoved, order: 3 },

packages/spec/src/migrations/registry.ts

@@ -5369,7 +5369,7 @@ const STEP18_RATIONALE: readonly RationaleFragment[] = [
   },
   {
     id: 'dataset-member-field-expression-refused',
-    order: 57,
+    order: 58,
     text:
       'It also holds an ADR-0021 dataset\'s `field` — `dimensions[].field` and `measures[].field` — to '
       + 'the accept set the cube members it compiles to already hold, from one shared declaration: a '