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.deps.json

@@ -0,0 +1,23 @@
+{
+  "runtimeTarget": {
+    "name": ".NETCoreApp,Version=v8.0",
+    "signature": ""
+  },
+  "compilationOptions": {},
+  "targets": {
+    ".NETCoreApp,Version=v8.0": {
+      "HwpToPdfConverter/2026.03.31": {
+        "runtime": {
+          "HwpToPdfConverter.dll": {}
+        }
+      }
+    }
+  },
+  "libraries": {
+    "HwpToPdfConverter/2026.03.31": {
+      "type": "project",
+      "serviceable": false,
+      "sha512": ""
+    }
+  }
+}