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/fr.ts

@@ -1047,6 +1047,7 @@ export const dict = {
   'sidebarFilesTree.menu.rename': 'Rebaptiser',
   'sidebarFilesTree.menu.copyPath': 'Copier le chemin',
   'sidebarFilesTree.menu.save': 'Sauvegarder',
+  'sidebarFilesTree.menu.download': 'Télécharger',
   'sidebarFilesTree.menu.newFile': 'Nouveau fichier',
   'sidebarFilesTree.menu.newFolder': 'Nouveau dossier',
   'sidebarFilesTree.menu.delete': 'Supprimer',