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/admin/AdminLayout.tsx

@@ -21,7 +21,9 @@ export function AdminLayout() {
                   to={item.to}
                   className={({ isActive }) =>
                     `block px-3 py-2 rounded-md text-sm font-medium whitespace-nowrap ${
-                      isActive ? 'bg-accent-900/40 text-accent-300' : 'hover:bg-surface-2'
+                      isActive
+                        ? 'bg-accent-900/40 text-accent-300 light:bg-accent-100 light:text-accent-700'
+                        : 'hover:bg-surface-2'
                     }`
                   }
                 >

frontend/src/components/admin/BulkImportModal.tsx

@@ -77,7 +77,7 @@ export function BulkImportModal({
             )}
 
             {result && (
-              <div className="p-3 bg-green-900/30 text-green-300 rounded-md text-sm">
+              <div className="p-3 bg-green-900/30 text-green-300 light:bg-green-100 light:text-green-800 rounded-md text-sm">
                 <p>
                   {createdLabel}: {result.created}, {updatedLabel}: {result.updated}
                 </p>