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/static/js/i18n.js

@@ -317,7 +317,9 @@ var I18N = {
   }
 };
 
-var currentLang = localStorage.getItem('pos_lang') || 'es';
+// Spanish is mandatory for all tenants; ignore any previously stored language.
+var currentLang = 'es';
+localStorage.setItem('pos_lang', 'es');
 
 /**
  * Translate a key to the current language.
@@ -328,12 +330,11 @@ window.t = function(key) {
 };
 
 /**
- * Switch the UI language and reload.
+ * Language switcher is disabled; the system stays in Spanish.
  */
 window.setLang = function(lang) {
-  currentLang = lang;
-  localStorage.setItem('pos_lang', lang);
-  location.reload();
+  currentLang = 'es';
+  localStorage.setItem('pos_lang', 'es');
 };
 
 /**