build(ci): add CodeQL workflow for Rust analysis

Uses advanced setup on windows-latest with an explicit build step
(cargo build --manifest-path src-egui/Cargo.toml) instead of
autobuild. Fixes low analysis quality from the default setup which
cannot resolve Windows-specific dependencies on a Linux runner.

Runs on push/PR to main and weekly on Mondays.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>