♻️ 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/agent/[id]/profile.vue

@@ -1,18 +1,12 @@
 <script setup lang="ts">
-const { getAgent, unsubscribe: unsubscribeAgents } = await useAgents();
+const { getAgent } = useAgents();
 const triplit = useTriplitClient();
 
 const route = useRoute();
 
-const agent = computed(() => {
-    if (route.params.id === null || typeof route.params.id !== 'string') {
-        throw new Error('Invalid agent ID');
-    }
+const agent = getAgent(route.params.id as string);
 
-    return getAgent(route.params.id)!;
-});
-
-// if (agent.value === undefined) navigateTo('/');
+if (agent.value === undefined) navigateTo('/');
 
 const handleInput = async (e: Event) => {
     const target = e.target as HTMLInputElement;
@@ -20,7 +14,7 @@ const handleInput = async (e: Event) => {
         return;
     }
 
-    await triplit.update('agents', agent.value.id, { name: target.value });
+    await triplit.update('agents', agent.value!.id, { name: target.value });
 };
 
 const changeSystemPrompt = async (e: Event) => {
@@ -31,14 +25,10 @@ const changeSystemPrompt = async (e: Event) => {
         value = undefined;
     }
 
-    await triplit.update('agents', agent.value.id, {
+    await triplit.update('agents', agent.value!.id, {
         systemPrompt: target.value,
     });
 };
-
-onUnmounted(() => {
-    unsubscribeAgents?.();
-});
 </script>
 
 <template>