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>

android/variables.gradle

@@ -0,0 +1,16 @@
+ext {
+    minSdkVersion = 24
+    compileSdkVersion = 36
+    targetSdkVersion = 36
+    androidxActivityVersion = '1.11.0'
+    androidxAppCompatVersion = '1.7.1'
+    androidxCoordinatorLayoutVersion = '1.3.0'
+    androidxCoreVersion = '1.17.0'
+    androidxFragmentVersion = '1.8.9'
+    coreSplashScreenVersion = '1.2.0'
+    androidxWebkitVersion = '1.14.0'
+    junitVersion = '4.13.2'
+    androidxJunitVersion = '1.3.0'
+    androidxEspressoCoreVersion = '3.7.0'
+    cordovaAndroidVersion = '14.0.1'
+}