v6.0.0 - paper 1.21.11 backport

This is a backport for paper 1.21.11

Breaking Changes

Paper 1.21.1 is now supported
Java 21 is now required (previously Java 17)
Removed integrations: BetonQuest, zNPCs, and ProjectKorra have been temporarily removed to keep notquests simple and easier to maintain. If you relied on BetonQuest conditions/events, zNPCs NPC linking, or ProjectKorra objectives, these are no longer available.

The entire GUI system has been rewritten with a new YAML-driven GUI framework
GUIs are now fully configurable via YAML files in the plugins/NotQuests/guis/ folder
Supports tabbed interfaces, paged item lists, and action buttons
Default GUIs included: main menu with tabs (active quests / take quests), quest preview, NPC quest selection, category browsing, and quest abort confirmation
Custom skull textures, dynamic placeholders (%QUESTNAME%, %CATEGORYNAME%, %PLAYER%, etc.), and per-item lore/display name from the language file
Powered by InvUI