- Restore allowed_chats gate before thread_id check so ignored_threads
applies universally (even to guest mentions).
- Compute _message_mentions_bot once in _should_process_message to
eliminate redundant second entity scan when guest_mode=true and the
message does not mention the bot.
- Remove redundant _is_group_chat from _is_guest_mention (caller already
verified the message is a group chat).
- Update _telegram_allowed_chats docstring to note guest_mode exception.
- Add test coverage: bot_command entity, text_mention entity,
caption_entities, and ignored_threads + guest_mode interaction.
- Add nik1t7n to AUTHOR_MAP.
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