♻️ 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/ChatInput.vue

@@ -1,10 +1,9 @@
 <script setup lang="ts">
 import { onMounted, ref, watch } from 'vue';
 import type { ModelWithProvider, ProviderWithModels } from '~/composables/useModels';
-import type { Entity } from '@triplit/client';
-import { schema } from '#triplit/schema';
+import type { Agent } from '~/composables/useAgents';
 
-const { allModels } = await useModels();
+const { allModels } = useModels();
 
 const inputHeight: Ref<string> = ref('auto');
 const inputRef = ref<HTMLTextAreaElement | null>(null);
@@ -19,7 +18,7 @@ const emit = defineEmits<{
 
 const props = defineProps<{
     loading?: boolean;
-    agent?: Entity<typeof schema, 'agents'>;
+    agent: Agent | null;
     providers?: ProviderWithModels[];
 }>();
 
@@ -107,6 +106,15 @@ const handleKeyDown = async (event: KeyboardEvent) => {
     }
 };
 
+const handleWindowKeyDown = async (event: KeyboardEvent) => {
+    if (event.ctrlKey || event.metaKey) {
+        return;
+    }
+
+    // redirect all standard keyboard input to the input field
+    inputRef.value?.focus();
+};
+
 watch(inputValue, async () => {
     const textarea = inputRef.value;
     if (!textarea) return;
@@ -141,6 +149,11 @@ onBeforeMount(() => {
 
 onMounted(() => {
     inputValue.value = tempInput;
+    document.addEventListener('keydown', handleWindowKeyDown);
+});
+
+onUnmounted(() => {
+    document.removeEventListener('keydown', handleWindowKeyDown);
 });
 </script>