Recreate Vulkan swapchain in LoadingScreen::render() when the dirty flag
is set, so resizing the window during world loading no longer renders
into a stale swapchain with mismatched framebuffers.
- 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