Add controlCenter widget: one-click quick settings popup

Single bar button (md-tune-vertical glyph) that opens a popup with the
controls most users reach for repeatedly throughout the day:

- Volume slider + mute toggle (Pipewire defaultAudioSink)
- Brightness slider (brightnessctl, coalesced via writeTimer)
- 2x2 tile grid: Do Not Disturb (makoctl mode), Night Light (omarchy-
  toggle-nightlight, temperature probed), Keep Awake (hypridle pid
  detection), Theme (current symlink + opens omarchy menu themes)
- Power-profile row (Saver / Balanced / Performance), hidden when
  power-profiles-daemon is not installed

Polled every 3s via Process + StdioCollector pairs gated by !running
busy checks. Default layout adds it before powerMenu on the right.

default/quickshell/bar/bar-defaults.json

@@ -5,7 +5,7 @@
   "layout": {
     "left": ["omarchy", "workspacesPro", "activeWindow"],
     "center": ["media", "calendar", "weatherFlyout", "update", "voxtype", "screenRecording", "idle", "notifications"],
-    "right": ["tray", "systemStats", "microphone", "bluetoothPanel", "networkPanel", "audioPanel", "nightLight", "brightness", "powerProfile", "battery", "powerMenu"]
+    "right": ["tray", "systemStats", "microphone", "bluetoothPanel", "networkPanel", "audioPanel", "nightLight", "brightness", "powerProfile", "battery", "controlCenter", "powerMenu"]
   },
   "modules": {
     "calendar": {