- Add vk-bootstrap as a git submodule (was in extern/ but not tracked,
causing "vk-bootstrap not found" on all CI jobs)
- Whitelist extern/vk-bootstrap in .gitignore
- Move stormlib to a separate optional install step on both Windows CI
jobs (mingw-w64-x86_64-stormlib doesn't exist in MSYS2 repos)
- Add loading screen system with stb_image for JPEG loading
- Two loading screen images (orc and dwarf) randomly selected
- Display loading screen while terrain data loads
- Cache WMO inverse matrices to reduce per-frame computation
- Stub WMO liquid rendering (needs coordinate system fix)
- Update spawn point to Stormwind Trade District