✨ feat(file-check): 添加 PLC 应答后命中文件删除

* 新增默认关闭的删除开关，仅在收到 PLC 放行应答后执行

* 本地与 SFTP Provider 校验根目录并支持幂等删除

* 补充工作流、设置页和文件删除相关测试与文档

tests/AxiOmron.PcbCheck.Tests/SystemSettingViewModelTests.cs

@@ -291,6 +291,11 @@ public sealed class SystemSettingViewModelTests
             throw new NotSupportedException();
         }
 
+        public Task<FileDeleteOutcome> DeleteMatchedFileAsync(string filePath, CancellationToken cancellationToken)
+        {
+            throw new NotSupportedException();
+        }
+
         public Task<FileCheckTestOutcome> TestConnectionAsync(AppConfig? config, CancellationToken cancellationToken)
         {
             return Task.FromResult(TestOutcome);