Add V2G library project and refactor code structure

- Create V2GProtocol.Library project for DLL usage by external programs
- Add V2GApi.cs with public API methods for EXI encoding/decoding
- Move helper functions to Helper.cs for better code organization
- Update project configuration for .NET Framework 4.8
- Translate all comments in Program.cs to Korean
- Fix .hex file handling to read as binary instead of text

🤖 Generated with [Claude Code](https://claude.ai/code)

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

V2GProtocol.Library.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Library</OutputType>
+    <TargetFramework>net48</TargetFramework>
+    <LangVersion>9.0</LangVersion>
+    <AssemblyName>V2GDecoder.Library</AssemblyName>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Remove="Program.cs" />
+  </ItemGroup>
+
+</Project>