fix: center button content vertically for square appearance

Reduce icon-label spacing and vertically center the content box
inside action buttons so they appear visually square.

src/moonset/panel.py

@@ -170,9 +170,10 @@ class PanelWindow(Gtk.ApplicationWindow):
     def _create_action_button(self, action_def: ActionDef) -> Gtk.Button:
         """Create a single action button with icon and label."""
         button_content = Gtk.Box(
-            orientation=Gtk.Orientation.VERTICAL, spacing=8
+            orientation=Gtk.Orientation.VERTICAL, spacing=4
         )
         button_content.set_halign(Gtk.Align.CENTER)
+        button_content.set_valign(Gtk.Align.CENTER)
 
         icon = Gtk.Image.new_from_icon_name(action_def.icon_name)
         icon.add_css_class("action-icon")

src/moonset/style.css

@@ -13,7 +13,7 @@ window.wallpaper {
     background-color: #1a1a2e;
 }
 
-/* Action button — 120x120px card */
+/* Action button — square card */
 .action-button {
     min-width: 120px;
     min-height: 120px;