Add third-party notices to desktop builds #41

Add third-party notices covering Bun's LGPL components, Electrobun binaries, Shiki grammars, and the provenance of packages/ui's WebGPU shader and dither code.

Status

packages/ui/NOTICE.md covers some UI notices, and some Sparkle/native licenses are acknowledged. Complete notices for redistributed Bun, Electrobun, Shiki and UI components, and the shader/dither provenance, are still outstanding or unverified in desktop builds.

Tracked by #7. Migrated from TODO.md — Release.