iPad: only the list tabs split into two columns

Home, Messages and Calls are lists that lead to a conversation, which is
what a second column is for. Everything else is a single screen, and
splitting those went badly: Files and the wallet pushed their unlock
screen into a column a third of the width, and the other two thirds said
"Pick a conversation" on a tab with no conversations in it. Account did
the same. Found in the 13-inch screenshot set.

Those tabs now take the whole width, the way a settings screen does on a
tablet. Whether a row opens beside the list or on top of it follows
whether the right-hand column is actually showing, so a row on a
full-width tab cannot open into a column that is not there.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Sources/Views/MainTabView.swift

@@ -18,6 +18,19 @@ struct MainTabView: View {
 
     private var isWide: Bool { sizeClass == .regular }
 
+    /// Home, Messages and Calls: the tabs that are lists leading to a
+    /// conversation, which is what a second column is for.
+    ///
+    /// Everything else is a single screen. Split, Files and the wallet pushed
+    /// their unlock screen into a column a third of the width, and the other
+    /// two thirds said "Pick a conversation" on a tab with no conversations in
+    /// it. Those take the whole width instead, the way a settings screen does
+    /// on a tablet.
+    private static let listTabs: Set<Int> = [0, 1, 2]
+
+    /// Two columns only when there is room for two AND this tab is a list.
+    private var usesSplit: Bool { isWide && Self.listTabs.contains(selection) }
+
     /// When the Calls tab was last opened, so the missed-call badge counts only
     /// what arrived since.
     @AppStorage("fnmsg.callsSeenAt") private var callsSeenAt: Double = 0
@@ -36,8 +49,12 @@ struct MainTabView: View {
             .environmentObject(pane)
             // One place decides, and everything downstream reads it. See
             // SplitPane.
+            .onChange(of: usesSplit, initial: true) { _, split in
+                // Whether a row opens beside the list or on top of it depends
+                // on whether the right-hand column is actually showing.
+                pane.isWide = split
+            }
             .onChange(of: isWide, initial: true) { _, wide in
-                pane.isWide = wide
                 // Coming back to one column, the conversation on the right has
                 // nowhere to be. Dropping it returns to the list rather than
                 // leaving a chat open that nothing on screen points at.
@@ -72,7 +89,7 @@ struct MainTabView: View {
     }
 
     @ViewBuilder private var layout: some View {
-        if isWide { wideLayout } else { tabs }
+        if usesSplit { wideLayout } else { tabs }
     }
 
     @ViewBuilder private var tabs: some View {