fix: handle stale chunk 404s + add page loading states

- Router catches failed dynamic imports and forces reload (stale deploy cache)
- LeaderboardPage: sprite-based loading animation while fetching
- ArenaPage: sprite-based loading animation while fetching

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

frontend/src/pages/ArenaPage.vue

@@ -45,8 +45,14 @@ const tierClass = (t: number) => `tier-${t}`
         <div></div>
       </div>
 
+      <!-- Loading -->
+      <div v-if="isLoading" class="flex-1 flex flex-col items-center justify-center gap-4">
+        <SpritePreview seed="loading" archetype="blob" :size="80" class="animate-bounce" />
+        <p class="font-display text-sm text-text-muted animate-pulse tracking-widest">LOADING FIGHTS...</p>
+      </div>
+
       <!-- Fight cards -->
-      <div class="flex-1 min-h-0 overflow-y-auto space-y-3">
+      <div v-else class="flex-1 min-h-0 overflow-y-auto space-y-3">
         <RouterLink
           v-for="fight in fights"
           :key="fight.id"

frontend/src/pages/LeaderboardPage.vue

@@ -52,8 +52,14 @@ const record = (b: Bot) => `${b.wins}W - ${b.losses}L`
         </span>
       </div>
 
+      <!-- Loading -->
+      <div v-if="isLoading" class="flex-1 flex flex-col items-center justify-center gap-4">
+        <SpritePreview seed="loading" archetype="standard" :size="80" class="animate-bounce" />
+        <p class="font-display text-sm text-text-muted animate-pulse tracking-widest">LOADING FIGHTERS...</p>
+      </div>
+
       <!-- Table -->
-      <div class="flex-1 min-h-0 overflow-y-auto border border-border rounded-lg bg-surface-raised/50">
+      <div v-else class="flex-1 min-h-0 overflow-y-auto border border-border rounded-lg bg-surface-raised/50">
         <table class="w-full">
           <thead class="sticky top-0 bg-surface-raised z-10">
             <tr class="border-b border-border text-text-muted font-display text-[10px] uppercase tracking-[0.15em]">