style(settings): grid the short cards, keep the tall ones stacked

Appearance and Account are both short — a LazyVGrid lets them sit
side-by-side when the window's wide enough instead of each wasting a
full-width row. Offline & Sync and About stay full-width: pairing
those with anything in the same grid row looked worse (very uneven
row heights) than just stacking them. Also widened the content column
(640 -> 900) so the grid actually has room to go two-up.

Outpost/Features/Account/SettingsView.swift

@@ -2,11 +2,11 @@
 import SwiftUI
 import OutlineKit
 
-/// Full-page Settings — rendered as a `RootView`-level overlay (see
-/// `AppNavigation`), not a separate popup window. Replaces the old
-/// `Settings {}` scene / `PreferencesView` and folds in what used to be the
-/// standalone "About Outpost" window's content too, so everything about the
-/// app lives in one place.
+/// Full-page Settings — swapped into `ContentView_macOS`'s detail pane (see
+/// `AppNavigation`), alongside the sidebar, not a separate popup window.
+/// Replaces the old `Settings {}` scene / `PreferencesView` and folds in
+/// what used to be the standalone "About Outpost" window's content too, so
+/// everything about the app lives in one place.
 struct SettingsView: View {
     let onDone: () -> Void
 
@@ -28,13 +28,21 @@ struct SettingsView: View {
             Divider()
             ScrollView {
                 VStack(alignment: .leading, spacing: 20) {
-                    appearanceSection
-                    accountSection
+                    // Appearance and Account are short — let them sit
+                    // side-by-side when there's room instead of each
+                    // claiming a full-width row on their own. Offline & Sync
+                    // and About stay full-width, own row each: both are
+                    // taller and visibly uneven height content, paired with
+                    // an adaptive grid, looks worse than just stacking.
+                    LazyVGrid(columns: [GridItem(.adaptive(minimum: 260), spacing: 20)], alignment: .leading, spacing: 20) {
+                        appearanceSection
+                        accountSection
+                    }
                     offlineSyncSection
                     aboutSection
                 }
                 .padding(24)
-                .frame(maxWidth: 640)
+                .frame(maxWidth: 900)
             }
             .frame(maxWidth: .infinity)
         }