ci: 将项目剩余工作流从 .NET Framework 迁移至 .NET 6

更新 README.md 中的运行环境要求，修改贡献指南中的目标分支
调整 CI/CD 工作流以适配 .NET 6 构建路径
移除安装程序中对 .NET Framework 的依赖检查

Signed-off-by: doudou0720 <98651603+doudou0720@users.noreply.github.com>

.github/workflows/prcheck.yml

@@ -3,7 +3,7 @@ name: PR Check
 on:
   pull_request:
     types: [opened, synchronize]
-    branches: [ main, beta ]
+    branches: [ main, net6 ]
     paths-ignore:
       - '**/*.md'
 
@@ -43,7 +43,7 @@ jobs:
       - name: Check if exe file is generated
         id: check-exe
         run: |
-          $exePath = "Ink Canvas\bin\Debug\${{ matrix.architecture }}\net472\InkCanvasForClass.exe"
+          $exePath = "Ink Canvas\bin\Debug\${{ matrix.architecture }}\net6.0-windows10.0.19041.0\InkCanvasForClass.exe"
           
           if (Test-Path $exePath) {
             echo "build_success=true" >> $env:GITHUB_OUTPUT
@@ -71,7 +71,7 @@ jobs:
         uses: actions/upload-artifact@v7
         with:
           name: InkCanvasForClass.CE.debug.${{ matrix.architecture }}
-          path: "Ink Canvas/bin/Debug/${{ matrix.architecture }}/net472/*"
+          path: "Ink Canvas/bin/Debug/${{ matrix.architecture }}/net6.0-windows10.0.19041.0/*"
         
 
       - name: Create Summary