Add post-game completion rule option

Add postGameCompletion toggle to nuzlocke rules so players can indicate
whether a run ends after the Champion or continues into post-game. Adds
a new "Completion" category section in rules configuration with a green
badge color.

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

frontend/src/components/RuleBadges.tsx

@@ -25,7 +25,9 @@ export function RuleBadges({ rules }: RuleBadgesProps) {
           className={`px-2 py-0.5 rounded-full text-xs font-medium ${
             def.category === 'core'
               ? 'bg-blue-100 text-blue-800 dark:bg-blue-900/40 dark:text-blue-300'
-              : 'bg-amber-100 text-amber-800 dark:bg-amber-900/40 dark:text-amber-300'
+              : def.category === 'completion'
+                ? 'bg-green-100 text-green-800 dark:bg-green-900/40 dark:text-green-300'
+                : 'bg-amber-100 text-amber-800 dark:bg-amber-900/40 dark:text-amber-300'
           }`}
         >
           {def.name}