Release v0.0.18

[awnion]

What's changed

Font

• Add cyrl-em = "hanging-serifless" variant
• Regenerate showcase images

CI/CD

• Rework release workflow: merge prerelease into pr.yaml, simplify release
• Add fork-release workflow for automatic builds on plan changes
• Cache Verda build artifacts between CI runs
• Bump upload-artifact to v7, download-artifact to v8, actions/cache to v5

Docs

• Add release process documentation (docs/RELEASING.md)
• Add homebrew install instructions, remove install_mac.sh
• Add homebrew cask template and update-tap script

Misc

• Rename docker_run.py to nerd-patcher.py
• Rename template for ruby syntax highlighting
• Skip fork-release workflow on the upstream repo