ci: restore full prerelease release assets

[matlux]

Summary

• restore the full GitHub prerelease asset list for binaries, checksums, and ts-proto tarball
• keep the prerelease-only trigger and document why the workflow intentionally avoids published
• fail the workflow if expected release assets are missing locally or not attached to the GitHub prerelease

Root cause

Commit 3acc90a added the canonical image job in the middle of the softprops/action-gh-release multiline files: block. The workflow stayed valid YAML, but the release upload list was truncated to veranad-linux-amd64 only.

Validation

• parsed .github/workflows/buildBinaries.yml successfully with Ruby YAML
• ran actionlint; it reported pre-existing workflow issues unrelated to this regression (old action versions and the existing github.event.inputs.NAME_SPACE reference), but no new syntax issue from this change

[pratikasr]

LGTM