Add CUDA 13.4 support and make release asset handling backend-aware

[thomas9120]

Summary

• Add Windows CUDA 13.4 backend support while retaining CUDA 13.3 as a legacy option.
• Require matching binary and runtime archives when listing, updating, or installing releases.
• Keep backend updates within the installed CUDA version and provide clearer errors when no compatible release exists.
• Add release lookup diagnostics and troubleshooting documentation.

Testing

• Added backend tests covering CUDA version separation, runtime requirements, bounded release paging, update behavior, and installation persistence.
• Updated existing route and backend specification test fixtures for required assets.