feat(pack): add typed theme contributions

[lusu007]

Pull Request

Description

Migrates library-gui from standalone resource-pack generation to typed Theme contributions backed by one deterministic internal plan.

• Adds Theme.toPackContribution(assets) with exact formats, vanilla-path claims, and the text-marker shader capability.
• Keeps writePack() and zipPack() as deprecated compatibility facades driven by the same plan.
• Moves final composition into the theme demo through ResourcePackComposer and ZipPackWriter.
• Serves immutable hash-addressed demo artifacts and keeps the production library dependency limited to resource-pack-api.

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• ♻️ Refactoring
• 📚 Documentation
• 🔧 Chore

Related Issues

• Relates to Resource Pack Contribution Migration Specification
• Relates to Resource Pack Contribution Migration Implementation Plan

Testing

• Unit tests pass
• Manual testing completed
• New tests added for new functionality
• Composite-build smoke and deterministic parity passed
• Clean published-package build passed against library-resource-pack:0.1.0
• Production JAR and runtime classpaths were inspected
• Runnable Minestom demo generated, hosted, and hashed the pack successfully

Checklist

• I have performed a self-review of my own code
• Tests have been added/updated and pass (if needed)
• Documentation has been updated (if needed)