Phase 1: wrap the reference web app in Capacitor for Android

Wraps reference/sp404-layers as a sideloadable APK without editing the
reference, which stays the frozen spec for the Phase 2 React port.

- sync-www.sh builds www/ from reference/ + native/, asserting each patch
  anchor so a reference change fails loudly rather than shipping broken
- drops the service worker (would serve a stale app after an APK update)
- haptics via a navigator.vibrate override, so buzz() needs no change
- localStorage mirrored into Preferences; sync load()/save() untouched
- hardware back: sheet -> Explore tab -> exit
- edge-to-edge handled in MainActivity: Android 16 + targetSdk 36 removes
  the opt-out, and a WebView never fills env(safe-area-inset-*), so insets
  are pushed into CSS custom properties instead

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,20 @@
+node_modules/
+
+# Generated by scripts/sync-www.sh from reference/ - never edit by hand.
+www/
+
+# Capacitor's generated Android project. Tracked selectively: the few files we
+# hand-edit (MainActivity, manifest, styles, variables.gradle) are force-added.
+android/.gradle/
+android/build/
+android/app/build/
+android/app/src/main/assets/public/
+android/app/src/main/assets/capacitor.config.json
+android/app/src/main/assets/capacitor.plugins.json
+android/capacitor-cordova-android-plugins/
+android/local.properties
+android/.idea/
+*.apk
+*.aab
+*.keystore
+!debug.keystore