feat: add PWA — mobile multi-model chat app (Vite + React)

- Vite + React + TypeScript + Tailwind v4
- vite-plugin-pwa for service worker and manifest
- Dark mode, borderless design with glow effects
- Reuses Elec components, adapted for mobile viewport
- Standalone-ready: can install to phone home screen

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

PWA/tailwind.config.js

@@ -0,0 +1,11 @@
+/** @type {import('tailwindcss').Config} */
+export default {
+  content: [
+    "./index.html",
+    "./src/**/*.{js,ts,jsx,tsx}",
+  ],
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+}