ver. 0.278: Settings + Languages frontend migration, bug fix get_single_settings_value

- Add cached frontend methods to existing Domain repositories (allSettings, getSingleValue, defaultLanguage, activeLanguages, translations)
- Convert front\factory\Settings and Languages to facades delegating to Domain repositories
- Fix get_single_settings_value() - was hardcoded to 'firm_name', now uses $param correctly
- Add CacheHandler stub methods (get/set/exists) to test bootstrap
- Establish architectural rule: Domain classes are shared between admin and frontend

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/bootstrap.php

@@ -78,6 +78,9 @@ if (!class_exists('Redis')) {
 
 if (!class_exists('CacheHandler')) {
     class CacheHandler {
+        public function get($key) { return null; }
+        public function set($key, $value, $ttl = 86400) {}
+        public function exists($key) { return false; }
         public function delete($key) {}
         public function deletePattern($pattern) {}
     }