Replace bar-settings with unified settings plugin

Consolidates bar-settings into a single 'settings' plugin with sidebar
categories: Defaults, Style, Bar, System, Plugins. Updates supporting
commands (omarchy-launch-settings, omarchy-style-corners-quickshell,
omarchy-theme-list-with-previews, omarchy-hyprland-monitor-scaling-set)
and refreshes sidebar glyphs to Nerd Font icons.

default/quickshell/omarchy-shell/plugins/bar/widgets/controlCenter.qml

@@ -362,11 +362,11 @@ Item {
       Common.PillButton {
         width: parent.width
         iconText: "󰙪"
-        text: "Customize bar…"
+        text: "Settings…"
         foreground: root.bar.foreground
         horizontalPadding: 10
         verticalPadding: 8
-        onClicked: { root.run("omarchy-launch-bar-settings"); root.popupOpen = false }
+        onClicked: { root.run("omarchy-launch-settings"); root.popupOpen = false }
       }
     }
   }