feat: add waybar module for package update notifications

Add moonarch-waybar-updates script that checks for available updates
from both official repos (checkupdates) and AUR (paru -Qua). Uses a
cache mechanism to avoid excessive mirror hits while still detecting
freshly installed updates within 60 seconds.

defaults/xdg/waybar/config

@@ -1,6 +1,6 @@
 {
     "__aboutme1": "Moonarch default waybar configuration for Niri.",
-    "__aboutme2": "User overrides go in ~/.config/waybar/config",
+    "__aboutme2": "Deployed to /etc/xdg/waybar/ by moonarch-git package.",
     "layer": "top",
     "margin-top": 0,
     "spacing": 5,
@@ -28,7 +28,7 @@
         "modules": [
             "custom/cpugov",
             "gamemode",
-            //"custom/updates",
+            "custom/updates",
             "idle_inhibitor",
             "custom/notification",
             "privacy"
@@ -205,9 +205,9 @@
             "has-updates": "󱍷",
             "updated": "󰂪"
         },
-        "exec-if": "which waybar-module-pacman-updates",
-        "exec": "waybar-module-pacman-updates",
-        "on-click": "alacritty paru"
+        "exec": "moonarch-waybar-updates",
+        "interval": 60,
+        "on-click": "foot paru"
     },
     "custom/notification": {
         "tooltip": true,