feat: 순수 .NET Provider 3종 (Data/Vector/ImageOptim) + Loss 분류 정확화

검증 가능한 순수 .NET 변환기를 우선 추가. 외부 도구 불필요, 실제 동작까지 테스트로 검증.

- DataProvider: csv<->json, csv<->xlsx 원자 엣지 (json<->xlsx는 그래프가 csv 경유 자동 합성). CsvHelper/ClosedXML
- VectorProvider: svg->png/pdf (svg->기타이미지는 png 경유 합성). Svg.Skia
- ImageOptimProvider: 동일포맷 재압축 self-edge (jpg/png/webp/tiff/bmp)
- Loss 분류 정확화: OCR·문서/HTML->이미지=Rasterize, ->pdf=Recode (멀티홉 이상경로 svg->pdf->docx->jpg 차단)
- 그래프 합성/실동작 테스트 9개 추가 (총 23개 통과)
- DocumentFormat.OpenXml 3.1.0->최신 (ClosedXML 호환)

src/Everything2Everything.Core/Everything2Everything.Core.csproj

@@ -12,15 +12,18 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="ClosedXML" Version="0.105.0" />
+    <PackageReference Include="CsvHelper" Version="33.1.0" />
     <PackageReference Include="Magick.NET-Q16-AnyCPU" Version="14.13.0" />
     <PackageReference Include="PDFtoImage" Version="5.2.1" />
     <PackageReference Include="PhotoSauce.MagicScaler" Version="0.15.0" />
     <PackageReference Include="PhotoSauce.NativeCodecs.Libheif" Version="1.19.5-preview1" />
     <PackageReference Include="Microsoft.Web.WebView2" Version="1.0.3912.50" />
-    <PackageReference Include="DocumentFormat.OpenXml" Version="3.1.0" />
+    <PackageReference Include="DocumentFormat.OpenXml" Version="3.5.1" />
     <PackageReference Include="Markdig" Version="0.37.0" />
     <PackageReference Include="ReverseMarkdown" Version="4.6.0" />
     <PackageReference Include="PDFsharp" Version="6.2.0" />
+    <PackageReference Include="Svg.Skia" Version="5.0.0" />
   </ItemGroup>
 
   <ItemGroup>