Remove unused nuzlocke rules, reorganize into core and playstyle

Remove firstEncounterOnly, permadeath, nicknameRequired, and
postGameCompletion from the rules system — they are either implicit
(it's a nuzlocke tracker) or not enforced. Move levelCaps to core
(it's displayed in the sticky bar). Create a new "playstyle" category
for hardcoreMode and setModeOnly — informational rules useful for
stats but not enforced by the tracker. Remove the completion category
entirely. Add sub-task beans for the rules overhaul epic.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/RuleBadges.tsx

@@ -21,9 +21,7 @@ export function RuleBadges({ rules }: RuleBadgesProps) {
           className={`px-2 py-0.5 rounded-full text-xs font-medium ${
             def.category === 'core'
               ? 'bg-blue-900/40 text-blue-300 light:bg-blue-100 light:text-blue-700'
-              : def.category === 'completion'
-                ? 'bg-green-900/40 text-green-300 light:bg-green-100 light:text-green-700'
-                : 'bg-amber-900/40 text-amber-300 light:bg-amber-100 light:text-amber-800'
+              : 'bg-purple-900/40 text-purple-300 light:bg-purple-100 light:text-purple-700'
           }`}
         >
           {def.name}