ui: neutral HTTP OTA placeholders, rename disconnect button

- HTTP OTA host/URI placeholders: megafon.ru -> example.com
- 'Disconnect from pySim' -> 'Disconnect from server'
  (RU: 'Отключиться от сервера')

SW cache v61 -> v62.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'otaman-v61';
+const CACHE = 'otaman-v62';
 const URLS = [
   'index.html',
   'help.html',