migrate to Preact and add iOS-feel animations

- Replace React 19 with Preact via @preact/preset-vite (zero component changes needed — Vite aliases react → preact/compat at build time)
- Add custom iOS easing curves (ease-ios, ease-spring) via Tailwind @theme
- Update all transitions to use iOS-standard 200ms durations and spring/decel easing
- Add active:scale press feedback on tiles, buttons, and toggles
- Toggle knob now uses spring easing for a satisfying snap

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

index.css

@@ -1 +1,6 @@
-@import "tailwindcss";
+@import "tailwindcss";
+
+@theme {
+  --ease-ios: cubic-bezier(0.25, 0.46, 0.45, 0.94);
+  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
+}