refactor(@angular/cli): consistent casing for onpush zoneless migration MCP tool name

All other tools use `_` in their names.

Author: cexbrayat

packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/zoneless-migration.ts

@@ -21,7 +21,7 @@ import { sendDebugMessage } from './send-debug-message';
 import { createSourceFile, getImportSpecifier } from './ts-utils';
 
 export const ZONELESS_MIGRATION_TOOL = declareTool({
-  name: 'onpush-zoneless-migration',
+  name: 'onpush_zoneless_migration',
   title: 'Plan migration to OnPush and/or zoneless',
   description: `
 <Purpose>