초기 커밋: Phase 1 — 레지스트리 기반 컨텍스트 메뉴 + 핵심 변환 파이프라인

- Provider 추상화(IConverterProvider + ProviderCapability) — Available/RequiresExternal/ComingSoon 1급 시민
- 변환 구현: Magick(이미지·RAW·GIF·TIFF), HEIC/HEIF(libheif decode→Magick encode), PDF(PDFium), DOCX(Word COM 또는 LibreOffice 자동 감지)
- ComingSoon 스텁: HTML, HWP/HWPX (UI 노출, 컨텍스트 메뉴 등록 자동 제외)
- WPF + WPF-UI 4.3 Fluent 2 UI: 메인 창(드래그&드롭, Provider 카드), 변환 창(썸네일·옵션·진행률), 빠른 변환 진행 창, 진단 창
- 단일 EXE에 verb 라우팅: quick / dialog / register / unregister / diagnose / help
- HKCU SystemFileAssociations 기반 컨텍스트 메뉴 등록 (Win11 "추가 옵션 표시"에 노출)
- README, packaging/ Phase 2 placeholder 포함

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/EverythingToJpeg.Core/OutputPathHelper.cs

@@ -0,0 +1,49 @@
+namespace EverythingToJpeg.Core;
+
+internal static class OutputPathHelper
+{
+    public static string ResolveOutputPath(
+        string outputDirectory,
+        string baseName,
+        string? pageSuffix,
+        NameCollision collision)
+    {
+        var safe = SanitizeFileName(baseName);
+        var fileName = string.IsNullOrEmpty(pageSuffix) ? $"{safe}.jpg" : $"{safe}{pageSuffix}.jpg";
+        var fullPath = Path.Combine(outputDirectory, fileName);
+
+        if (!File.Exists(fullPath)) return fullPath;
+
+        switch (collision)
+        {
+            case NameCollision.Overwrite:
+                return fullPath;
+            case NameCollision.Skip:
+                return fullPath;
+            case NameCollision.AppendNumber:
+            default:
+                for (var i = 1; i < 10000; i++)
+                {
+                    var candidate = string.IsNullOrEmpty(pageSuffix)
+                        ? Path.Combine(outputDirectory, $"{safe} ({i}).jpg")
+                        : Path.Combine(outputDirectory, $"{safe}{pageSuffix} ({i}).jpg");
+                    if (!File.Exists(candidate)) return candidate;
+                }
+                return fullPath;
+        }
+    }
+
+    public static bool ShouldSkip(string finalPath, NameCollision collision)
+        => collision == NameCollision.Skip && File.Exists(finalPath);
+
+    private static string SanitizeFileName(string name)
+    {
+        var invalid = Path.GetInvalidFileNameChars();
+        Span<char> buffer = stackalloc char[name.Length];
+        for (var i = 0; i < name.Length; i++)
+        {
+            buffer[i] = Array.IndexOf(invalid, name[i]) >= 0 ? '_' : name[i];
+        }
+        return new string(buffer);
+    }
+}