Custom Head Overrides

• Added override: true option for custom head definitions to replace bundled heads with the same ID
• Without the override flag, duplicate head IDs still error to prevent accidental conflicts
• Plugin now logs a summary of replaced heads when custom overrides are applied
• Updated README with documentation on custom heads and override usage

Silk Touch Drop Rules

• Mini blocks made from valuable materials (diamond, emerald, gold, netherite) now have conditional drop rules
• Without Silk Touch: Drops the vanilla block material
• With Silk Touch: Drops the mini block head
• This applies to both base mini blocks and alphabet blocks derived from these materials (but not to other heads, like gold chalices)
• Added valuable_drop_materials configuration in generate_config.toml
• Updated generation scripts to support drop sections for valuable materials