feat: Complete cross-platform build system and folder reorganization

- Reorganize project structure: Port/ → DotNet/, VC/, C++/
- Add comprehensive cross-platform build automation
  - Windows: build_all.bat, build.bat files for all components
  - Linux/macOS: build_all.sh, build.sh files for all components
- Update all build scripts with correct folder paths
- Create test automation scripts (test_all.bat/sh)
- Update documentation to reflect new structure
- Maintain 100% roundtrip accuracy for test5.exi (pure EXI)
- Support both Windows MSBuild and Linux GCC compilation

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

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

C++/build.bat

@@ -0,0 +1,20 @@
+@echo off
+echo Building V2GDecoder...
+
+gcc -o V2GDecoder V2GDecoder.c ^
+    src/iso1/*.c ^
+    src/iso2/*.c ^
+    src/din/*.c ^
+    src/codec/*.c ^
+    -I./src/codec ^
+    -I./src/iso1 ^
+    -I./src/iso2 ^
+    -I./src/din
+
+if %ERRORLEVEL% EQU 0 (
+    echo Build successful! V2GDecoder.exe created.
+) else (
+    echo Build failed with error code %ERRORLEVEL%
+)
+
+pause