♻️ 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/assets/css/base.css

@@ -57,15 +57,15 @@
 }
 
 :root.dark {
-    --palette-zinc-100: #09080A;
-    --palette-zinc-200: #1a191b;
-    --palette-zinc-300: #2e2d2f;
+    --palette-zinc-100: #09080D;
+    --palette-zinc-200: #1a191E;
+    --palette-zinc-300: #2e2d32;
     --palette-slate-100: #0f171c;
     --palette-slate-200: #1e252b;
     --palette-slate-300: #333b44;
-    --palette-obsidian-100: #050504;
-    --palette-obsidian-200: #0f0f0e;
-    --palette-obsidian-300: #1e1f1f;
+    --palette-obsidian-100: #050307;
+    --palette-obsidian-200: #0f0e11;
+    --palette-obsidian-300: #1e1d20;
 
     --text-primary: color-mix(in srgb, #fafafa, var(--color-accent) var(--accent-hinting));
     /* Selected topics */
@@ -177,6 +177,8 @@ html.light {
 
 html {
     height: 100vh;
+    /* something something progressive enhancement */
+    height: 100dvh;
     overflow: hidden;
 }
 
@@ -270,6 +272,11 @@ button.accent:hover {
     transform: translateX(calc(2.5em - 1.3em - 0.5rem));
 }
 
+:where(.i-tabler\:dots) {
+    background-color: currentColor;
+    mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' width='18' height='18'%3E%3Cpath fill='none' stroke='black' stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='M4 12a1 1 0 1 0 2 0a1 1 0 1 0-2 0m7 0a1 1 0 1 0 2 0a1 1 0 1 0-2 0m7 0a1 1 0 1 0 2 0a1 1 0 1 0-2 0'/%3E%3C/svg%3E");
+}
+
 .reasoning-contaizner.middle {
     mask-image: linear-gradient(#000, #000, transparent 0, #000 12%, #000 88%, transparent)
 }
@@ -465,16 +472,4 @@ article .checkbox {
     width: min-content;
 }
 
-/* end markdown renderer */
-
-.reasoning-contaizner.middle {
-    mask-image: linear-gradient(#000, #000, transparent 0, #000 12%, #000 88%, transparent)
-}
-
-.reasoning-contaizner.top {
-    mask-image: linear-gradient(#000, transparent, #000 0, #000 12%, #000 88%, transparent)
-}
-
-.reasoning-contaizner.bottom {
-    mask-image: linear-gradient(transparent, #000, transparent 0, #000 12%, #000 88%, #000)
-}
+/* end markdown renderer */