docs: LT Wahl controls, file upload, updated next steps

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

client/app/README.md

@@ -48,8 +48,12 @@ Teamer login only).
   - Gemeinden (list/create); each opens **Teamer-Verwaltung**
     (`teamer_admin_screen.dart`): local Teamer accounts + group-link / email
     invites.
-  - **Workshop-Wahlen** (`wahl_admin_screen.dart`): create Wahlen, add
-    workshops, run the assignment, view the result table.
+  - **Workshop-Wahlen** (`wahl_admin_screen.dart`): create Wahlen, open/close
+    them, add workshops, list participants + Force-Zuteilung, run the
+    assignment, view the result table, export the CSV (browser download).
+  - **Dateien** (`files_admin_screen.dart`): upload with a visibility tier
+    (native `<input type=file>`), list. Needs a configured Nextcloud/S3 on
+    the backend or the upload returns 500.
   - pending Verantwortlichen self-registrations (approve / reject).
 - **Als Verantwortliche/r registrieren**
   (`verantwortliche_register_screen.dart`) — shown on the home screen to a