V18.2 Custom Emoji Render Fix
- Fixed the test mappings so they work even when bot_element_emojis is empty.
- Admin/database rows override built-in mappings.
- Message text is rendered as Telegram <tg-emoji> entities.
- Button mappings are applied through the keyboard markup path; supported inline/button clients receive native icon metadata.
- No user/order/balance data is changed by this patch.