feat: add chat topic binding for casual conversation

Add ability to bind a dedicated chat topic where normal conversation
happens, separate from functional topics (purchases, payments, etc.)

- Add 'chat' to HOUSEHOLD_TOPIC_ROLES
- Add /bind_chat_topic command for admins
- Update i18n strings for en/ru
- Add command to admin scope in telegram-commands

apps/bot/src/telegram-commands.ts

@@ -35,6 +35,7 @@ const GROUP_ADMIN_COMMAND_NAMES = [
   ...GROUP_MEMBER_COMMAND_NAMES,
   'setup',
   'unsetup',
+  'bind_chat_topic',
   'bind_purchase_topic',
   'bind_feedback_topic',
   'bind_reminders_topic',