feat: introduce AirApp SDK, InkCanvas components, and background service infrastructure with updated dependencies

NuGet.Config

@@ -1,5 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
+  <packageSources>
+    <clear />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+  </packageSources>
   <config>
     <!-- 相对本文件：包落在仓库目录下，与仓库同盘（本机 D:），避免依赖 C:\Temp\cursor-sandbox-cache 等易损路径 -->
     <add key="globalPackagesFolder" value=".nuget/packages" />