feat: Clarify GH Actions

[initstring]

Summary

• Run the CI workflow on every PR (regardless of target branch) so linting, type-checking, tests, and build validation always execute.
• Rename and split the Docker automation into two workflows: PRs now use “Validate Docker Build” (build-only), while releases use “Publish Docker Image” with explicit GHCR push wording.

Testing

• Workflow definition lint via act -l (optional).
• CI will validate on next PR; release workflow remains unchanged functionally aside from naming.