- Channels tab is now a drill-down on iPhone: ChannelBrowserView lists top-level
channels; ChannelDetailView shows the people in a channel, its sub-channels, and
an explicit Join button (with password prompt). iPad split view unchanged.
- Extract self-contained UserRow (context menu + sheets) from UserListView so admin
actions are reused in the drill-down.
- Fix off-screen chat compose box: pin VoiceControlsView via per-tab
.safeAreaInset(edge: .bottom) instead of a floating overlay, so it reserves layout
space above the tab bar (keeping the compose box visible, cooperating with keyboard
avoidance) without covering the tab bar buttons.
- Collapse Activity into Chat like macOS/Windows: ChatView renders a merged,
time-sorted timeline of messages + activity (activity rows in gray); remove the
Activity tab and ActivityLogView.
- Label the RPSystemBroadcastPickerView inner UIButton for VoiceOver
("Share/Stop sharing screen audio") instead of relying on an outer SwiftUI label.
