[macOS] Fix SDL threading issues and add full macOS support

[codearranger]

• Move SDL operations to main thread to fix NSWindow threading errors
• Add SDL_MAIN_HANDLED macro for macOS builds
• Implement proper event processing in main game loop
• Update documentation to reflect working macOS status
• Add .gitattributes for consistent line endings across platforms
• Add CLAUDE.md with project instructions for AI assistance
• Ignore custom font file in .gitignore

The SDL version now runs correctly on macOS with all threading issues resolved. Font fallback system automatically uses system fonts when custom font is unavailable.

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