文件名清理改为固定的 Windows 非法字符集，Linux CI 现在也会将 : 替换为 -。

清除了 DOCX 测试的空引用警告，以及 3 处 xUnit Assert.Single 分析器警告。

tests/Jiaowu.Api.Tests/GradeAnalysisWordReportGeneratorTests.cs

@@ -43,16 +43,19 @@ public sealed class GradeAnalysisWordReportGeneratorTests
         Assert.True(bytes.Length > 10_000);
         using var stream = new MemoryStream(bytes);
         using var document = WordprocessingDocument.Open(stream, false);
-        var text = document.MainDocumentPart!.Document.InnerText;
+        var mainDocumentPart = document.MainDocumentPart
+            ?? throw new InvalidOperationException("Generated document has no main document part.");
+        var text = mainDocumentPart.Document?.InnerText
+            ?? throw new InvalidOperationException("Generated document has no document body.");
         Assert.Contains("成绩分析报告", text);
         Assert.Contains("同课程教学班对比", text);
         Assert.Contains("各范围基准", text);
         Assert.Contains("历年成绩趋势", text);
         Assert.Contains("行政班组成", text);
         Assert.Contains("计科一班", text);
-        Assert.Equal(3, document.MainDocumentPart.ImageParts.Count());
-        Assert.Equal(2, document.MainDocumentPart.HeaderParts.Count());
-        Assert.Equal(2, document.MainDocumentPart.FooterParts.Count());
+        Assert.Equal(3, mainDocumentPart.ImageParts.Count());
+        Assert.Equal(2, mainDocumentPart.HeaderParts.Count());
+        Assert.Equal(2, mainDocumentPart.FooterParts.Count());
     }
 
     [Fact]
@@ -76,10 +79,13 @@ public sealed class GradeAnalysisWordReportGeneratorTests
         Assert.True(bytes.Length > 8_000);
         using var stream = new MemoryStream(bytes);
         using var document = WordprocessingDocument.Open(stream, false);
-        var text = document.MainDocumentPart!.Document.InnerText;
+        var mainDocumentPart = document.MainDocumentPart
+            ?? throw new InvalidOperationException("Generated document has no main document part.");
+        var text = mainDocumentPart.Document?.InnerText
+            ?? throw new InvalidOperationException("Generated document has no document body.");
         Assert.Contains("科目总体成绩分析报告", text);
         Assert.Contains("学生来源学院对比", text);
         Assert.Contains("教学班横向比较", text);
-        Assert.Single(document.MainDocumentPart.ImageParts);
+        Assert.Single(mainDocumentPart.ImageParts);
     }
 }