make hat bar full-width, separators 1px visible

Hat bar is now a single continuous row above the three columns
instead of per-column segments. Left: macOS traffic lights or
empty. Center: project > branch. Right: minimize/maximize/close
on Linux or empty. Column separators keep 4px hit area but show
a 1px centered line.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

linux/runner/my_application.cc

@@ -25,11 +25,12 @@ static void my_application_activate(GApplication* application) {
   GtkWindow* window =
       GTK_WINDOW(gtk_application_window_new(GTK_APPLICATION(application)));
 
-  // D-057: frameless custom chrome. The Flutter app draws its own
-  // per-column hats with drag regions and window buttons.
+  // D-057: frameless custom chrome — the Flutter app draws its own
+  // hat bar with drag regions and window buttons.
   gtk_window_set_decorated(window, FALSE);
   gtk_window_set_title(window, "clide");
 
+
   gtk_window_set_default_size(window, 1280, 720);
 
   // Window icon — load from the bundled asset.