Add native macOS application support

[ppapak]

Summary

• build and package the Qt 6 UI as a native macOS application bundle
• enable MoltenVK portability enumeration for Apple GPUs
• bundle Video2X models, Qt frameworks, and native dependencies
• add macOS power/config handling and a reproducible build script
• document the macOS build workflow
• update encoder stream-copy fields for the current Video2X core API

Depends on the macOS core support in k4yt3x/video2x#1511.

Verification

• built on Apple M3 Pro with Qt 6.11.1
• launched the generated Video2X.app successfully
• verified the complete bundle with codesign --verify --deep --strict