Add modular interactive widgets to the Quickshell bar

Introduces a widgets/ directory of first-party QML modules and a common/
helpers library. Widgets auto-load by name from
default/quickshell/bar/widgets/<name>.qml — no edits to shell.qml needed
for additions beyond the firstPartyWidgets registry.

New widgets (all orientation-aware, top/bottom/left/right):
- media: MPRIS now-playing with scrolling label, cover art popup,
  play/pause/skip controls
- audioPanel: master volume slider, output device picker, per-app mixer
- networkPanel: Wi-Fi scan + connect, current connection details
- bluetoothPanel: paired device list, connect/disconnect, battery
- calendar: month grid popup keyed to today
- notificationCenter: live notification feed, DND toggle, clear all
- brightness: slider popup with scroll-to-adjust
- powerProfile: power-saver/balanced/performance picker (UPower)
- systemStats: inline CPU + RAM sparklines, expanded popup with btop
- weatherFlyout: weather popup with refresh and full report
- workspacesPro: animated focus indicator that slides between workspaces
- powerMenu: lock/suspend/log out/reboot/shutdown popup
- idleInhibitor: coffee-cup toggle wired to omarchy-toggle-idle
- microphone: mic state + mute toggle + scroll volume

Common helpers (default/quickshell/bar/common/):
- WidgetButton: hover/press scale animation, tooltip integration
- PopupCard: orientation-aware anchor + slide-in opacity transition
- Slider: drag/wheel-able linear slider with knob hover bump
- PillButton: rounded action button with icon + label

Bar root gains requestPopout/releasePopout so only one popup is open at
a time across widgets.

Updates bar-defaults.json to ship the new widgets out of the box while
keeping the legacy modules available.

default/quickshell/bar/common/WidgetButton.qml

@@ -0,0 +1,69 @@
+import QtQuick
+
+Item {
+  id: root
+
+  property var bar: null
+  property string text: ""
+  property string fontFamily: bar ? bar.fontFamily : "JetBrainsMono Nerd Font"
+  property real fontSize: 12
+  property color foreground: bar ? bar.foreground : "#cacccc"
+  property color activeColor: bar ? bar.urgent : "#a55555"
+  property bool active: false
+  property real horizontalMargin: 7.5
+  property real verticalPadding: 6
+  property real fixedWidth: -1
+  property real fixedHeight: -1
+  property real textRotation: 0
+  property bool keepSpace: false
+  property string tooltipText: ""
+  property real hoverScale: 1.0
+  property real pressScale: 0.92
+
+  signal pressed(int button)
+  signal wheelMoved(int delta)
+
+  readonly property bool vertical: bar ? bar.vertical : false
+  readonly property int barSize: bar ? bar.barSize : 26
+
+  visible: text !== "" || keepSpace
+  opacity: text === "" ? 0 : 1
+  implicitWidth: fixedWidth > 0 ? fixedWidth : (vertical ? barSize : Math.max(12, label.implicitWidth + horizontalMargin * 2))
+  implicitHeight: fixedHeight > 0 ? fixedHeight : (vertical ? Math.max(12, label.implicitHeight + verticalPadding * 2) : barSize)
+
+  Behavior on opacity {
+    NumberAnimation { duration: 140; easing.type: Easing.OutCubic }
+  }
+
+  Text {
+    id: label
+    anchors.centerIn: parent
+    text: root.text
+    color: root.active ? root.activeColor : root.foreground
+    font.family: root.fontFamily
+    font.pixelSize: root.fontSize
+    rotation: root.textRotation
+    horizontalAlignment: Text.AlignHCenter
+    verticalAlignment: Text.AlignVCenter
+    scale: mouseArea.pressed ? root.pressScale : (mouseArea.containsMouse ? root.hoverScale : 1.0)
+
+    Behavior on color {
+      ColorAnimation { duration: 160 }
+    }
+
+    Behavior on scale {
+      NumberAnimation { duration: 110; easing.type: Easing.OutCubic }
+    }
+  }
+
+  MouseArea {
+    id: mouseArea
+    anchors.fill: parent
+    acceptedButtons: Qt.LeftButton | Qt.RightButton | Qt.MiddleButton
+    hoverEnabled: true
+    onEntered: if (root.bar) root.bar.showTooltip(root, root.tooltipText)
+    onExited: if (root.bar) root.bar.hideTooltip(root)
+    onClicked: function(mouse) { root.pressed(mouse.button) }
+    onWheel: function(wheel) { root.wheelMoved(wheel.angleDelta.y) }
+  }
+}