feat: move-to-root, active tab highlight, show-in-explorer for all file items

- Add 'Move to root' context menu item for non-root sidebar tree nodes
- Improve active tab visual contrast (background + font-weight)
- FileTreeRow: show-in-explorer inline button & context menu for all items
- OpenFolder now resolves file-type nodes to parent directory
- handleShowInFolder uses item.nodeId || item.id for FileDTO compatibility
- Add i18n key nav.moveToRoot (ru/en)

frontend/src/lib/i18n/locales/en.js

@@ -16,6 +16,7 @@ export default {
   'nav.openFolder': 'Open folder',
   'nav.createInside': 'Create inside',
   'nav.createNode': 'Create element',
+  'nav.moveToRoot': 'Move to root',
   'nav.selectPrompt': 'Select a section or case',
   'nav.brand': 'Verstak',
 

frontend/src/lib/i18n/locales/ru.js

@@ -21,6 +21,7 @@ export default {
   'nav.openFolder': 'Открыть папку',
   'nav.createInside': 'Создать внутри',
   'nav.createNode': 'Создать элемент',
+  'nav.moveToRoot': 'Переместить в корень',
 
   'tab.overview': 'Обзор',
   'tab.notes': 'Заметки',