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

.gitignore

@@ -0,0 +1,36 @@
+# Dependencies
+node_modules/
+
+# Build output
+dist/
+
+# Tauri
+src-tauri/target/
+src-tauri/gen/schemas
+src-tauri/Cargo.lock
+
+# Environment files
+.env
+.env.*
+!.env.example
+
+# Logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+
+# Editor directories
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Sisyphus session files
+.sisyphus/