feat(bar): floating center area for widgets

* Added a new floating area at the center of the bar
* Optional center widgets config, fixed spacing on the center widget
* Turning transparency on by default

komorebi-bar/src/config.rs

@@ -37,6 +37,8 @@ pub struct KomobarConfig {
     pub grouping: Option<Grouping>,
     /// Left side widgets (ordered left-to-right)
     pub left_widgets: Vec<WidgetConfig>,
+    /// Center widgets (ordered left-to-right)
+    pub center_widgets: Option<Vec<WidgetConfig>>,
     /// Right side widgets (ordered left-to-right)
     pub right_widgets: Vec<WidgetConfig>,
 }