Migrate pinenote-shell to AGS v3/Astal framework

Replace the custom GJS/GTK4 @agi/gtk3 setup with AGS v3 on GTK3 using
Astal services (Hyprland, Brightness). Updates README installation
instructions, package scripts, and rewrites main.js to use AGS JSX
widgets and reactive state bindings. Adds a minimal package-lock.json.

pinenote-shell/package.json

@@ -5,10 +5,8 @@
   "main": "./src/main.js",
   "type": "module",
   "scripts": {
-    "start": "gjs src/main.js",
-    "dev": "gjs --interpret src/main.js"
+    "start": "ags run src/main.js",
+    "dev": "ags run src/main.js"
   },
-  "dependencies": {
-    "@agi/gtk3": "^0.7.4"
-  }
+  "dependencies": {}
 }