Publish reproducible Vision v8 ONNX release artifacts

[Complexity-ML]

Context

PR #10 documents the expected Vision v8 O2M and NMS-free ONNX binaries, metadata sidecars, sizes, and SHA-256 hashes, but the binaries are intentionally not stored in Git.

We need a reproducible release path so users can download verified artifacts without relying on a one-off local export.

Scope

• Add a manual or tag-triggered GitHub Actions workflow for Vision ONNX releases.
• Pin the source checkpoint repository and revision.
• Export both o2m and nms-free with the documented opset.
• Run ONNX validation and parity checks before publishing.
• Generate a machine-readable manifest containing checkpoint revision, framework commit, opset, input/output contract, file sizes, and SHA-256 hashes.
• Upload both .onnx files, both JSON sidecars, and the manifest as GitHub Release assets.
• Link the release from the validation report.

Acceptance criteria

• A failed export, parity gate, or checksum verification prevents publication.
• Published assets can be reproduced from the documented commit and checkpoint revision.
• ONNX binaries remain excluded from normal source commits.
• Release notes distinguish O2M (decode + NMS) from NMS-free (decode + confidence filtering).
• Artifact hashes match the release manifest.

Related: #10