Add GPU-ready asset upload staging

[edisonlee0212]

Summary

• Add staged GPU-ready asset loading so published assets can remain pending until GPU upload/finalization completes.
• Route runtime Texture2D updates and geometry storage uploads through tracked GPU-service work, including dirty-range geometry uploads.
• Update loading UI/readback/shutdown readiness handling and add coverage for asset readiness, texture uploads, geometry publication, and buffer subrange uploads.

Validation

• python Scripts\format_cpp.py --check
• git diff --check
• python Scripts\test.py --all --config RelWithDebInfo passed 26/26 after rebasing to latest dev.