fix: include legacy 'firecracker' asset in GitHub releases

[tomassrnka]

Summary

• Copy amd64 binary as both firecracker-amd64 and firecracker in GitHub releases
• Ensures existing consumers that reference the old firecracker asset name continue to work

Test plan

• Verify new releases contain three assets: firecracker, firecracker-amd64, firecracker-arm64
• Verify firecracker and firecracker-amd64 are identical binaries

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Low risk: only adjusts the GitHub Actions release packaging/upload logic, with no runtime code changes; main risk is unintended release asset naming/overwriting via --clobber.

Overview
GitHub release creation now publishes an additional legacy firecracker asset by copying the amd64 binary to both firecracker-amd64 and firecracker.

The workflow also broadens the upload/create globs from firecracker-* to firecracker*, so existing releases can be backfilled/updated with the new legacy asset (and any updated binaries) using gh release upload --clobber.

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[cursor]

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