feat(*): add native macOS CLI support

[ppapak]

Summary

• add Apple linker and FFmpeg path handling
• support Vulkan portability enumeration through MoltenVK
• use native macOS executable-path discovery for installed models
• add a reproducible Apple Silicon build script
• document native macOS CLI installation and usage

Verification

• built Video2X 6.4.0 on Apple Silicon macOS
• detected an Apple M3 Pro through MoltenVK
• initialized Real-ESRGAN from outside the source directory

Scope

Tested on Apple Silicon (arm64) macOS.