refactor: convert SPA to multi-page architecture

- Add scene_onboarding.html, scene_dashboard.html, scene_settings.html
- Add onboarding.js, dashboard.js, settings.js scripts
- Update vite.config.js for multi-page build
- Navigation via window.location.href between pages
- Bottom nav bar on dashboard only

tailwind.config.js

@@ -1,6 +1,6 @@
 /** @type {import('tailwindcss').Config} */
 module.exports = {
-  content: ["./index.html", "./scene_*.html"],
+  content: ["./src/**/*.{html,js}"],
   theme: {
     extend: {
       colors: {