Fix WCAG AA color contrast violations across all pages

Replace incorrect perceived-brightness formula in Stats progress bars
with proper WCAG relative luminance calculation, and convert type bar
colors to hex values for reliable contrast detection. Add light: variant
classes to status badges, yellow/purple text, and admin nav links across
17 files. Darken light-mode status-active token and text-tertiary/muted
tokens. Add aria-labels to admin filter selects and flex-wrap for mobile
overflow on AdminEvolutions.

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

frontend/src/components/ShinyBox.tsx

@@ -9,7 +9,7 @@ interface ShinyBoxProps {
 export function ShinyBox({ encounters, onEncounterClick }: ShinyBoxProps) {
   return (
     <div className="border-2 border-yellow-600 rounded-lg p-4">
-      <h3 className="text-sm font-semibold text-yellow-400 mb-3 flex items-center gap-1.5">
+      <h3 className="text-sm font-semibold text-yellow-400 light:text-amber-700 mb-3 flex items-center gap-1.5">
         <span>&#10022;</span>
         Shiny Box
         <span className="text-xs font-normal text-text-muted ml-1">