Address momus review: fix icons, vertical layout, popup coordination

- Replace nerd font glyphs that were stripped during the initial widget
  writes with verified codepoints sourced from the JetBrains Mono Nerd
  Font cmap (cpu-64-bit, scale-balance, notification-clear-all, etc).
- systemStats now switches to a Column layout when the bar is vertical
  so the widget no longer overflows a 28px-wide side bar.
- Remove notificationCenter from defaults: it registers a notification
  server and would collide with the mako daemon Omarchy autostarts.
- PopupCard owns the popout coordinator lifecycle and delegates close to
  its widget owner when provided; calendar and media now pass owner.
- brightness debounces brightnessctl writes through a coalescing timer
  to avoid spawning a process per slider tick.
- audioPanel tracks unfiltered Pipewire sinks/streams via PwObjectTracker
  so audio metadata becomes available before filtering.
- ModuleSlot re-injects bar/moduleName/settings whenever the bar config
  serial changes so widget settings update live with bar.json.
- Guard null bar references in workspacesPro and systemStats components
  that are constructed before bar injection.

default/quickshell/bar/widgets/calendar.qml

@@ -68,6 +68,7 @@ Item {
     id: popup
     anchorItem: button
     bar: root.bar
+    owner: root
     open: root.popupOpen
     contentWidth: 300
     contentHeight: header.implicitHeight + grid.implicitHeight + 36
@@ -85,7 +86,7 @@ Item {
           id: prevButton
           anchors.left: parent.left
           anchors.verticalCenter: parent.verticalCenter
-          iconText: ""
+          iconText: "󰅁"
           foreground: root.bar.foreground
           horizontalPadding: 8
           verticalPadding: 4
@@ -105,7 +106,7 @@ Item {
           id: nextButton
           anchors.right: parent.right
           anchors.verticalCenter: parent.verticalCenter
-          iconText: ""
+          iconText: "󰅂"
           foreground: root.bar.foreground
           horizontalPadding: 8
           verticalPadding: 4