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

src-tauri/src/lib.rs

@@ -0,0 +1,6 @@
+#[cfg_attr(mobile, tauri::mobile_entry_point)]
+pub fn run() {
+  tauri::Builder::default()
+    .run(tauri::generate_context!())
+    .expect("error while running tauri application");
+}