♻️ refactor: optimize state management, switch to @tanstack/vue-virtual, and improve performance

- Centralize `useAgents` and `useModels` state within the Nuxt app context to prevent data leaks and improve initialization.
- Migrate virtualization from `vue-virtual-scroller` to `@tanstack/vue-virtual` with new `RowVirtualizerFixed` and `RowVirtualizerDynamic` components.
- Upgrade Nuxt to v4.3.1 and remove `@vue-macros/nuxt`.
- Replace `big.js` with an optimized custom `lshDecimal` string manipulation logic for pricing calculations in the provider API.
- Implement automatic focus redirection in `ChatInput` to capture standard keyboard input.
- Refactor Sidenav and Settings components to utilize virtualization for long lists (topics, agents, models).
- Enhance theme colors and mobile experience. More work to come on both of these.

app/pages/index.vue

@@ -1,12 +1,11 @@
 <script setup lang="ts">
-import type schema from '#triplit/schema';
-import type { Entity } from '@triplit/client';
 import { assert } from '~~/utils/assert';
+import type { Agent } from '~/composables/useAgents';
 
 const triplit = useTriplitClient();
 
-const { agents, unsubscribe: unsubscribeAgents, createAgent } = await useAgents();
-const { providers, unsubscribe: unsubscribeModels, getFirstAvailableModel, allModels } = await useModels();
+const { agents, createAgent } = useAgents();
+const { providers, getFirstAvailableModel, allModels } = useModels();
 
 const taglines = {
     morning: [
@@ -74,12 +73,12 @@ const typeWriter = (time: 'morning' | 'afternoon' | 'evening') => {
 };
 
 const agent = computed(() => {
-    return agents.value?.[0];
+    return agents.value?.[0] ?? null;
 });
 
 const handleChatSubmit = async (message: string, model: ModelWithProvider | null) => {
     console.log('Message submitted:', message, agents);
-    let agent: Entity<typeof schema, 'agents'> | null = agents.value?.[0] ?? null;
+    let agent: Agent | null = agents.value?.[0] ?? null;
     if (!agent) {
         const triplit = useTriplitClient();
         assert('flush' in triplit);
@@ -162,8 +161,6 @@ onUnmounted(() => {
     if (typeWriterInterval !== null) {
         clearTimeout(typeWriterInterval);
     }
-    unsubscribeAgents?.();
-    unsubscribeModels?.();
 })
 </script>