Show discovered devices and shrink bluetooth header buttons

- Scan and Manage are now small icon-only buttons in the header beside
  the On/Off pill, with hover tooltips via the new PillButton.tooltipText
  prop (backed by QtQuick.Controls ToolTip).
- New discoveredDevices list pulls everything in Bluetooth.devices that
  isn't paired/connected/bonded/trusted. While scanning, those appear
  under a 'Discovered' header. Click pairs and connects.
- Empty-state text only shows when there are no known and no
  discovered devices, otherwise it would push down real entries.

default/quickshell/omarchy-shell/plugins/bar/common/PillButton.qml

@@ -1,10 +1,12 @@
 import QtQuick
+import QtQuick.Controls
 
 Rectangle {
   id: root
 
   property string text: ""
   property string iconText: ""
+  property string tooltipText: ""
   property color foreground: "#cacccc"
   property color background: "transparent"
   property color hoverBackground: Qt.rgba(foreground.r, foreground.g, foreground.b, 0.12)
@@ -17,6 +19,10 @@ Rectangle {
   property bool active: false
   property color activeBackground: Qt.rgba(foreground.r, foreground.g, foreground.b, 0.18)
 
+  ToolTip.visible: tooltipText !== "" && mouseArea.containsMouse
+  ToolTip.text: tooltipText
+  ToolTip.delay: 400
+
   signal clicked()
   signal rightClicked()