Add vale directives around Importmap term

Wrap the Asset architecture section heading and the paragraph containing
"Importmap" with vale off/on directives to suppress the Vale spelling error.

Author: promptless[bot]

docs/development-environment/building_assets.rst

@@ -52,11 +52,19 @@ Bootstrap framework
 
 Mautic uses Bootstrap 3.4.1 for its UI framework. The Bootstrap source files come from the ``twbs/bootstrap-sass`` Composer package and are available for importing in your SCSS files.
 
+.. vale off
+
 Asset architecture
 ==================
 
+.. vale on
+
+.. vale off
+
 Mautic uses Symfony Asset Mapper and Importmap for managing frontend JavaScript modules. The Asset Mapper configuration lives in ``app/config/config.php`` and the import map in ``importmap.php``.
 
+.. vale on
+
 .. vale off
 
 Compiled CSS outputs to ``var/sass/``. Asset Mapper serves it through Symfony's asset system in development. Production builds copy finalized assets to ``media/css/``.