Move plugins to manifest, pin Docker version, add Makefile

- Add plugins.txt listing all plugins for reproducible installs
- Add Makefile with setup/start/stop/install-plugins targets
- Remove user/plugins/ from git tracking
- Pin Docker image to 1.7.49.5-ls244

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

plugins/flex-objects/languages/ru.yaml

@@ -1,12 +0,0 @@
-PLUGIN_FLEX_OBJECTS:
-  PLUGIN_NAME: "Flex Objects"
-  PLUGIN_DESCRIPTION: "Плагин Flex Objects позволяет управлять объектами Flex через плагин админки."
-
-  USE_BUILT_IN_CSS: "Использовать встроенный CSS"
-  EXTRA_ADMIN_TWIG_PATH: "Дополнительный путь к шаблонам Twig"
-  DIRECTORIES: "Каталоги"
-
-  STATE:
-    CREATED_SUCCESSFULLY: "Успешно создано"
-    UPDATED_SUCCESSFULLY: "Успешно обновлено"
-    DELETED_SUCCESSFULLY: "Успешно удалено"