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/widgets/microphone.qml

@@ -0,0 +1,56 @@
+import QtQuick
+import Quickshell
+import Quickshell.Services.Pipewire
+import "../common" as Common
+
+Item {
+  id: root
+
+  property QtObject bar: null
+  property string moduleName: "microphone"
+  property var settings: ({})
+
+  readonly property var source: Pipewire.defaultAudioSource
+  readonly property bool muted: source && source.audio ? source.audio.muted : true
+  readonly property real volume: source && source.audio ? source.audio.volume : 0
+  readonly property var nodes: Pipewire.nodes ? Pipewire.nodes.values : []
+
+  readonly property var activeStreams: {
+    var list = []
+    for (var i = 0; i < nodes.length; i++) {
+      var node = nodes[i]
+      if (node && node.isStream && node.isSink === false && !node.audio?.muted) list.push(node)
+    }
+    return list
+  }
+
+  readonly property bool inUse: activeStreams.length > 0 && !muted
+
+  visible: source !== null
+  implicitWidth: button.implicitWidth
+  implicitHeight: button.implicitHeight
+
+  function toggleMute() {
+    if (source && source.audio) source.audio.muted = !source.audio.muted
+  }
+
+  PwObjectTracker { objects: root.source ? [root.source] : [] }
+
+  Common.WidgetButton {
+    id: button
+    anchors.fill: parent
+    bar: root.bar
+    text: root.muted ? "󰍭" : "󰍬"
+    active: root.inUse
+    tooltipText: root.muted ? "Microphone muted" : (root.inUse ? "Microphone in use" : "Microphone live")
+    onPressed: function(b) {
+      if (b === Qt.MiddleButton) root.bar.run("omarchy-launch-audio")
+      else root.toggleMute()
+    }
+    onWheelMoved: function(delta) {
+      if (!root.source || !root.source.audio) return
+      var step = 0.05
+      root.source.audio.volume = Math.max(0, Math.min(1, root.volume + (delta > 0 ? step : -step)))
+    }
+  }
+}