Theseus Quests

• Added Markdown description editing with formatting, links, colors, object insertion, undo/redo, and split preview.
• Added rich description rendering for styles, links, registry objects, and hover text. Unedited legacy content remains unchanged.
• Added registered custom icons for quests, tasks, and rewards, with unknown icon data preserved.
• Locked quests now explain whether access is blocked by policy or unmet prerequisites. Visible prerequisites can be selected.

Known issues:

• May currently have issues launching under Neoforge versions 26.2.0.87, 26.2.0.88. Version 26.2.0.86 is tested and works.