- Replace showRPGAttributes boolean with rpgAttributes array in trackerConfig
- Add RPG Attributes section in Edit Trackers with add/remove/rename/toggle
- Dynamically generate attribute display from config in userStats.js
- Add migration from old showRPGAttributes to new rpgAttributes array
- Initialize new attributes with default value of 10 in classicStats
- Default attributes: STR, DEX, CON, INT, WIS, CHA (all enabled)