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>

build/InkCanvasForClass CE.iss

@@ -59,13 +59,5 @@ Name: "{group}\{cm:ProgramOnTheWeb,{#MyAppName}}"; Filename: "{#MyAppURL}"
 Name: "{group}\{cm:UninstallProgram,{#MyAppName}}"; Filename: "{uninstallexe}"
 Name: "{autodesktop}\{#MyAppName}"; Filename: "{app}\{#MyAppExeName}"; Tasks: desktopicon
 
-[Code]
-function InitializeSetup: Boolean;
-begin
-  Result := True; // Always allow setup to continue
-  if not IsDotNetInstalled(net472, 0) then // Check if .NET Framework version 4.7.2 or compatible is installed
-    SuppressibleMsgBox('警告：未检测到 .NET Framework 4.7.2 或更高版本。应用程序可能无法正常运行。', mbInformation, MB_OK, IDOK);
-end;
-
 [Run]
 Filename: "{app}\{#MyAppExeName}"; Description: "{cm:LaunchProgram,{#StringChange(MyAppName, '&', '&&')}}"; Flags: nowait postinstall skipifsilent