Fix GitHub Actions YAML parsing: lowercase registry owner and quote hex keys

[MontrealAI]

Motivation

• Fix invalid workflow errors caused by the unsupported toLower(github.repository_owner) expression and YAML parsing hex literals as integers.
• Ensure the Docker image tags receive a lowercased registry owner value available at runtime instead of relying on an unsupported workflow expression.
• Prevent YAML from interpreting demo private keys as integers by preserving them as strings.

Description

• Remove the unsupported toLower(github.repository_owner) env usage and add a Set registry owner step that runs echo "REGISTRY_OWNER=${GITHUB_REPOSITORY_OWNER,,}" >> "$GITHUB_ENV" to set REGISTRY_OWNER.
• Quote hex private keys in .github/workflows/demo-zenith-hypernova.yml and .github/workflows/demo-zenith-sapience-omnidominion.yml so they are treated as strings (e.g. PRIVATE_KEY: '0x...').
• Continue using REGISTRY_OWNER when tagging images in the release.yml workflow so tags remain ghcr.io/${{ env.REGISTRY_OWNER }}/${{ matrix.name }}:....

Testing

• No automated tests were run because these are workflow-only YAML changes; CI workflows will validate the files when executed.

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Codex Task