Online world entry now shows a progress bar during character model,
terrain, and tile streaming. Fixed loading screen crash from calling
ImGui::NewFrame while a frame was already in progress. Log file is
now truncated on each launch instead of appending.
- 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