* android, desktop, ios: remove right gap on received messages in channels
In channels received messages now use the full row width instead of the chat-bubble right gap, matching the broadcast/feed style. Gated on ChatInfo.isChannel (useRelays), the always-present channel flag used across the channel UI; sent messages and non-channel groups, business and direct chats are unchanged.
* docs: add plan justifying removing right gap on received messages in channels
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Co-authored-by: Evgeny Poberezkin <evgeny@poberezkin.com>