fix(directory-explorer): make batch add work in VS Code; add Turkish locale keys

Two non-blockers from the openchamber-bot review at b2ab4af15:

1. VS Code batch add reported a misleading failure. addProjects
   returned [] unconditionally for the VS Code runtime because
   addWorkspaceFolder is reached only by addProject. Iterate addProject
   per path so valid selections succeed and the host is called once
   per selection. addProjects is now async (returns Promise<ProjectEntry[]>);
   the call site in DirectoryExplorerDialog awaits it; existing
   tests in useProjectsStore.test.ts updated to await.

2. Turkish locale (tr.ts) was missing the two new keys that other
   11 dictionaries received: actions.addSelected and browse.selectForAdd.
   Add both with real Turkish translations: "Seçilenleri ekle" and
   "Eklemek için seç".

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

@@ -1775,6 +1775,7 @@ export const dict = {
   'directoryExplorerDialog.actions.openInFinder': 'Finder\'da aç',
   'directoryExplorerDialog.actions.adding': 'Ekleniyor...',
   'directoryExplorerDialog.actions.addProject': 'Proje ekle',
+  'directoryExplorerDialog.actions.addSelected': 'Seçilenleri ekle',
   'directoryExplorerDialog.actions.addLocalProject': 'Yerel proje ekle',
   'directoryExplorerDialog.actions.cloneRepository': 'Depoyu klonla',
   'directoryExplorerDialog.actions.cloneAndAdd': 'Klonla ve ekle',
@@ -1791,6 +1792,7 @@ export const dict = {
   'directoryExplorerDialog.browse.retry': 'Yeniden dene',
   'directoryExplorerDialog.browse.parentDirectory': 'Üst dizin',
   'directoryExplorerDialog.browse.addedBadge': 'Eklendi',
+  'directoryExplorerDialog.browse.selectForAdd': 'Eklemek için seç',
   'directoryExplorerDialog.browse.quickAdd': 'Ekle',
   'directoryExplorerDialog.footer.navigate': 'Gezin',
   'directoryExplorerDialog.footer.select': 'Seç',