Publish verified Windows CUDA release sidecars

[leehack]

Summary

• replace the slow Windows x64 source-built CUDA matrix lane with verified upstream llama.cpp CUDA 12.4 and CUDA 13.3 sidecars
• bind each sidecar to the exact native release tag, llama.cpp commit, and same-run ggml-base.dll SHA-256
• version backend/runtime filenames so CUDA 12 and CUDA 13 can coexist without mixing dependency families
• publish the two verified sidecars through the normal release artifact and assets.json provenance flow
• retain the non-publishing experiment path for fast packaging-contract validation

The dependent Dart consumer is leehack/llamadart#340. Runtime downloading is intentionally out of scope and tracked in leehack/llamadart#339.

Why

The source-built CUDA lane dominated Windows release time even though upstream llama.cpp already publishes matching CUDA binaries. The previous experiment proved that the exact b10453 assets can be repackaged and loader-smoked without a GPU in about four minutes; this change moves that measured path into the owning native release workflow while preserving an exact compatibility boundary with the locally built core.

Validation

• 18 CUDA contract/package/verification unit tests passed
• release provenance contracts passed
• workflow YAML parse passed
• actionlint -shellcheck= passed
• git diff --check passed
• non-publishing exact-head experiment: https://github.com/leehack/llamadart-native/actions/runs/32041342903
  • exact b10453 provenance and asset digests verified
  • CUDA 12.4 and 13.3 fatbins inspected
  • CUDA 13 loader smoke passed without a GPU
  • CUDA 12 correctly reported the missing NVIDIA driver on the GPU-less runner

Publication gates

This PR remains draft. No native release has been published and no physical NVIDIA GPU was available. Before publication, validate representative CUDA 12/13 hardware and real-model inference, including kernel/PTX execution and the open MTP acceptance, CUDA lockup, DFlash concurrency, DSpark VRAM-leak, EAGLE, and failed-state-restore reports.

Tracked by #64.