♻️ 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/components/Message/Agent/Tool/Debug.vue

@@ -1,4 +1,4 @@
-<script lang="ts" setup>
+<script setup lang="ts">
 import type { Entity } from '@triplit/client';
 import type schema from '#triplit/schema';
 

app/components/Message/Agent/Tool/index.vue

@@ -1,4 +1,4 @@
-<script lang="ts" setup>
+<script setup lang="ts">
 import type { Entity } from '@triplit/client';
 import type schema from '#triplit/schema';
 import Debug from './Debug.vue';