Chat overhaul: send queue, mentions, scroll, mobile, live member list

Messages you try to send while offline or during a reconnect no longer get lost — they queue up and send automatically when the connection returns, and any that fail outright surface in a small tray above the composer with retry and discard buttons. Mentions are now first-class: typing @ pops an autocomplete picker for members, @everyone, and @here, and the mentioned member actually gets a notification instead of just seeing a styled name. Channels remember your scroll position when you switch away and back, a New divider stays visible at your last-read point until you scroll past it, jumping to a referenced message briefly highlights the target so you can spot it, and images and embeds reserve their space before they finish loading so the message list stops jumping. Mobile gets swipe-from-edge sidebars, an emoji picker that opens as a bottom sheet, a composer that stays above the iOS keyboard, larger touch targets in the chat header and composer toolbar, long-press on a message to open the same action menu desktop hover shows, swipe-right-to-reply on message rows, and a camera-capture option in the attachment picker. The member sidebar now reflects bans, unbans, sign-ups, role grants, and account deletions the moment they happen for everyone connected instead of lagging behind a periodic refresh, switching channels on a large server no longer re-fetches the full roster every time, and role badges on chat messages from members who have left the server now render correctly instead of falling back to a default look.