feat: HwpToPdfConverter exe 추가, .gitignore 설정

- HwpToHwpxConverter_260420/: HWP→HWPX 변환 exe 및 의존 파일 포함
- .gitignore: __pycache__, input/, test_output/, .venv/, *.zip 제외

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

HwpToHwpxConverter_260420/HwpToPdfConverter.runtimeconfig.json

@@ -0,0 +1,20 @@
+{
+  "runtimeOptions": {
+    "tfm": "net8.0",
+    "frameworks": [
+      {
+        "name": "Microsoft.NETCore.App",
+        "version": "8.0.0"
+      },
+      {
+        "name": "Microsoft.WindowsDesktop.App",
+        "version": "8.0.0"
+      }
+    ],
+    "configProperties": {
+      "System.Reflection.Metadata.MetadataUpdater.IsSupported": false,
+      "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": true,
+      "CSWINRT_USE_WINDOWS_UI_XAML_PROJECTIONS": false
+    }
+  }
+}