Improve run creation workflow with filters, local box art, and sticky nav

Use local /boxart/{slug}.png images instead of database boxArtUrl with
color-swatch fallback. Add region filter pills and run-status checkboxes
(hide active/completed) to GameGrid. Move the Next button into a sticky
top bar showing selected game summary so it's always visible. Capitalize
region names in all display locations.

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

frontend/src/pages/admin/AdminGameDetail.tsx

@@ -152,7 +152,7 @@ export function AdminGameDetail() {
       <div className="mb-6">
         <h2 className="text-xl font-semibold">{game.name}</h2>
         <p className="text-sm text-gray-500 dark:text-gray-400">
-          {game.region} &middot; Gen {game.generation}
+          {game.region.charAt(0).toUpperCase() + game.region.slice(1)} &middot; Gen {game.generation}
           {game.releaseYear ? ` \u00b7 ${game.releaseYear}` : ''}
         </p>
       </div>