feat: complete Linux support — add 40+ missing FFI functions, fix XlibWindowHandle type

The Linux native layer was missing all scene graph, lighting, shadows,
post-processing, projection, and picking functions that were already
present in macOS/Windows/iOS. Also fixes XlibWindowHandle::new() taking
c_ulong (u64) not u32, and removes 7 duplicate function declarations
from package.json.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Ralph Kuepper