fix(app): drop fullscreen control from About/Keyboard Shortcuts windows

SwiftUI's Window scene defaults to a full titlebar with a fullscreen
button even for small fixed-size reference panels that have no reason
to support it, matching neither platform convention nor how the main
app window is styled.

Outpost/OutpostApp.swift

@@ -54,11 +54,13 @@ struct OutpostApp: App {
         #if os(macOS)
         Window("About Outpost", id: "about") {
             AboutView()
+                .disablesFullScreen()
         }
         .windowResizability(.contentSize)
 
         Window("Keyboard Shortcuts", id: "keyboard-shortcuts") {
             KeyboardShortcutsView()
+                .disablesFullScreen()
         }
         .windowResizability(.contentSize)
 

Outpost/Support/WindowConfigurator.swift

@@ -0,0 +1,38 @@
+#if os(macOS)
+import SwiftUI
+import AppKit
+
+/// Grabs the hosting `NSWindow` once it's attached to a screen, for the
+/// handful of things SwiftUI's `Window` scene doesn't expose a modifier for.
+private struct WindowConfigurator: NSViewRepresentable {
+    let configure: (NSWindow) -> Void
+
+    func makeNSView(context: Context) -> NSView {
+        let view = NSView()
+        DispatchQueue.main.async {
+            if let window = view.window {
+                configure(window)
+            }
+        }
+        return view
+    }
+
+    func updateNSView(_ nsView: NSView, context: Context) {}
+}
+
+extension View {
+    /// `Window` scenes default to a full standard titlebar, fullscreen
+    /// (green) button included — not appropriate for fixed-size reference
+    /// panels like About or Keyboard Shortcuts, which have no reason to
+    /// support fullscreen at all.
+    func disablesFullScreen() -> some View {
+        background(
+            WindowConfigurator { window in
+                window.collectionBehavior.remove(.fullScreenPrimary)
+                window.collectionBehavior.insert(.fullScreenNone)
+                window.standardWindowButton(.zoomButton)?.isHidden = true
+            }
+        )
+    }
+}
+#endif