feat(i18n): force Spanish as the only language across all tenants

- i18n.js now locks currentLang to 'es' and overwrites pos_lang in localStorage.

- Disabled setLang language switching.

- Removed ES/EN toggle from sidebar.

- Bumped i18n.js and sidebar.js cache version on all templates.

pos/templates/dashboard.html

@@ -595,11 +595,11 @@
 
 
   <script src="/pos/static/js/chart.umd.min.js" defer></script>
-  <script src="/pos/static/js/i18n.js" defer></script>
+  <script src="/pos/static/js/i18n.js?v=36" defer></script>
   <script src="/pos/static/js/app-init.js" defer></script>
   <script src="/pos/static/js/splash-loader.js?v=33" defer></script>
   <script src="/pos/static/js/pos-utils.js?v=33" defer></script>
-  <script src="/pos/static/js/sidebar.js" defer></script>
+  <script src="/pos/static/js/sidebar.js?v=36" defer></script>
   <script src="/pos/static/js/dashboard-stats.js?v=33" defer></script>
   <script src="/pos/static/js/dashboard.js?v=33" defer></script>
   <script src="/pos/static/js/sync-engine.js" defer></script>