fix(files): hide desktop-only reveal action and label download in browser clients

Reveal-in-file-manager was always offered whenever the server exposed
revealPath, including in a plain browser tab where there is no local
file manager to reveal into. Gate it behind a new isBrowserClientRuntime
check (web platform, no Electron shell) and relabel the save action to
"Download" for that case, since it triggers a browser-style file
download rather than an in-place save.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packages/ui/src/lib/i18n/messages/uk.ts

@@ -1191,6 +1191,7 @@ export const dict: Record<I18nKey, string> = {
   "sidebarFilesTree.menu.rename": "Перейменувати",
   "sidebarFilesTree.menu.copyPath": "Копіювати шлях",
   "sidebarFilesTree.menu.save": "Зберегти",
+  "sidebarFilesTree.menu.download": "Завантажити",
   "sidebarFilesTree.menu.newFile": "Новий файл",
   "sidebarFilesTree.menu.newFolder": "Нова папка",
   "sidebarFilesTree.menu.delete": "Видалити",