Set default asset to BTC in Leaderboard (matching LiveView)

src/views/LeaderboardView.vue

@@ -185,7 +185,8 @@ export default {
         this.filters.names = state.nameOptions.map(o => o.value)
       }
       if (!this.filters.assets.length && state.assetOptions.length) {
-        this.filters.assets = state.assetOptions.map(o => o.value)
+        // Default to BTC (matching LiveView default)
+        this.filters.assets = ['BTC']
       }
       if (!this.filters.models.length && state.modelOptions.length) {
         this.filters.models = state.modelOptions.map(o => o.value)