WinUI plugin enhancements and add MVVM Toolkit skill (#1643)

* WinUI plugin enhancements and mvvm toolkit skill

* Split mvvm-toolkit skill for slimming

plugins/winui3-development/.github/plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "winui3-development",
-  "description": "WinUI 3 and Windows App SDK development agent, instructions, and migration guide. Prevents common UWP API misuse and guides correct WinUI 3 patterns for desktop Windows apps.",
-  "version": "1.0.0",
+  "description": "End-to-end WinUI 3 and Windows App SDK toolkit: expert agent, coding instructions, UWP-to-WinUI 3 migration guide, MVVM Toolkit reference, plus CLIs for packaging/debugging (winapp) and Microsoft Store publishing (msstore). Covers the full write → package → publish lifecycle for desktop Windows apps and prevents common UWP API misuse.",
+  "version": "1.2.0",
   "author": {
     "name": "Awesome Copilot Community"
   },
@@ -13,12 +13,20 @@
     "windows-app-sdk",
     "xaml",
     "desktop",
-    "windows"
+    "windows",
+    "mvvm",
+    "msix",
+    "microsoft-store"
   ],
   "agents": [
     "./agents/winui3-expert.md"
   ],
   "skills": [
+    "./skills/msstore-cli/",
+    "./skills/mvvm-toolkit-di/",
+    "./skills/mvvm-toolkit-messenger/",
+    "./skills/mvvm-toolkit/",
+    "./skills/winapp-cli/",
     "./skills/winui3-migration-guide/"
   ]
 }