feat(client/linux): preferences at 830 px — category tabs in the header bar

AdwPreferencesDialog parks its view switcher in a bottom bar whenever the
dialog is narrower than 110pt × page count (≈ 733 px for our five pages),
and the default float width (~640 px) is always under that — so the tabs
could never reach the header. 830 px puts them there for good (the tabbed
look the Apple and Windows clients share) with margin to spare, and gives
the caption-bearing rows room to breathe. A window too small to grant the
width still collapses the switcher to the bottom bar on its own.

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

clients/linux/src/ui_settings.rs

@@ -365,6 +365,11 @@ pub fn show(
     let dialog = adw::PreferencesDialog::new();
     dialog.set_title("Preferences");
     dialog.set_search_enabled(true);
+    // Wide enough that the category switcher sits in the HEADER BAR (the tabbed look the
+    // Apple/Windows clients have): AdwPreferencesDialog moves it to a bottom bar below a
+    // breakpoint of 110pt × page count (≈ 733 px for our five pages). In a window that
+    // can't give the dialog this width it still collapses to the bottom bar on its own.
+    dialog.set_content_width(830);
     let inline = gamescope_session();
 
     // ---- Display: Resolution ----