feat(ios): iPhone channel drill-down, fix chat compose box, unify chat+activity

- 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.

clients/apple/iOS/VoiceCatiOS/Views/UserListView.swift

@@ -3,11 +3,6 @@ import VoiceCatCore
 
 struct UserListView: View {
     @Bindable var session: SessionState
-    @State private var selectedUser: User?
-    @State private var showPerUserTuning = false
-    @State private var showBanUser = false
-    @State private var showMoveUser = false
-    @State private var showPermissions = false
 
     var body: some View {
         let channelUsers = session.currentChannelId == 0
@@ -15,10 +10,7 @@ struct UserListView: View {
             : session.users.filter { $0.channelId == session.currentChannelId }
 
         List(channelUsers) { user in
-            UserRowView(user: user, isSelf: user.id == session.selfUserId)
-                .contextMenu {
-                    userContextMenu(user: user)
-                }
+            UserRow(user: user, session: session)
         }
         .listStyle(.plain)
         .overlay {
@@ -30,115 +22,5 @@ struct UserListView: View {
                 )
             }
         }
-        .sheet(item: $selectedUser) { user in
-            if showPerUserTuning {
-                PerUserTuningView(user: user, session: session)
-            } else if showBanUser {
-                BanUserView(user: user, session: session)
-            } else if showMoveUser {
-                MoveUserView(user: user, session: session)
-            } else if showPermissions {
-                PermissionsView(user: user, session: session)
-            }
-        }
-    }
-
-    @ViewBuilder
-    private func userContextMenu(user: User) -> some View {
-        if user.id != session.selfUserId {
-            Button {
-                selectedUser = user
-                showPerUserTuning = true
-                showBanUser = false; showMoveUser = false; showPermissions = false
-            } label: {
-                Label("Volume / NR", systemImage: "speaker.wave.2")
-            }
-            if session.permissions.canKick || session.permissions.isAdmin {
-                Divider()
-                Button {
-                    session.kickUser(user.id, reason: "")
-                } label: {
-                    Label("Kick", systemImage: "person.fill.xmark")
-                }
-                if session.permissions.canBan || session.permissions.isAdmin {
-                    Button(role: .destructive) {
-                        selectedUser = user
-                        showBanUser = true
-                        showPerUserTuning = false; showMoveUser = false; showPermissions = false
-                    } label: {
-                        Label("Ban…", systemImage: "nosign")
-                    }
-                }
-            }
-            if session.permissions.canMoveUsers || session.permissions.isAdmin {
-                Button {
-                    selectedUser = user
-                    showMoveUser = true
-                    showPerUserTuning = false; showBanUser = false; showPermissions = false
-                } label: {
-                    Label("Move to channel…", systemImage: "arrow.right.circle")
-                }
-            }
-            if session.permissions.isAdmin {
-                Divider()
-                let muted = user.serverMuted
-                Button {
-                    session.setServerMute(user.id, muted: !muted, deafened: user.serverDeafened)
-                } label: {
-                    Label(muted ? "Unmute" : "Server Mute", systemImage: muted ? "mic" : "mic.slash")
-                }
-                Button {
-                    selectedUser = user
-                    showPermissions = true
-                    showPerUserTuning = false; showBanUser = false; showMoveUser = false
-                } label: {
-                    Label("Permissions…", systemImage: "lock.shield")
-                }
-            }
-        }
-    }
-}
-
-private struct UserRowView: View {
-    let user: User
-    let isSelf: Bool
-
-    var body: some View {
-        HStack(spacing: 10) {
-            Image(systemName: user.selfMicMuted || user.serverMuted ? "mic.slash.fill" : "mic.fill")
-                .foregroundStyle(user.selfMicMuted || user.serverMuted ? .red : .green)
-                .imageScale(.small)
-                .accessibilityHidden(true)
-            VStack(alignment: .leading, spacing: 1) {
-                HStack(spacing: 4) {
-                    Text(user.nickname)
-                        .fontWeight(isSelf ? .semibold : .regular)
-                    if isSelf {
-                        Text("(you)")
-                            .font(.caption2)
-                            .foregroundStyle(.secondary)
-                    }
-                    if user.isGuest {
-                        Text("guest")
-                            .font(.caption2)
-                            .foregroundStyle(.secondary)
-                    }
-                }
-                if user.serverMuted || user.serverDeafened {
-                    Text(user.serverDeafened ? "server deafened" : "server muted")
-                        .font(.caption2)
-                        .foregroundStyle(.orange)
-                }
-            }
-            Spacer()
-            if user.selfDeafened {
-                Image(systemName: "headphones.slash")
-                    .imageScale(.small)
-                    .foregroundStyle(.secondary)
-                    .accessibilityHidden(true)
-            }
-        }
-        .accessibilityElement(children: .combine)
-        .accessibilityLabel("\(user.nickname)\(isSelf ? ", you" : "")\(user.isGuest ? ", guest" : "")\(user.selfMicMuted ? ", muted" : "")\(user.serverMuted ? ", server muted" : "")")
     }
 }