feat(android): Capacitor wrapper bundling the Fabric web frontend

Greenfield Android client built as a Capacitor shell (mirrors the
Desktop strategy — reuses the React SPA 100%):
- appId ai.hangman.fabric, appName Fabric, androidScheme http +
  usesCleartextTraffic (talks to the http Center/Guild backends; the
  login screen sets the Center base, so a phone points at a LAN/host
  URL instead of localhost).
- scripts/build-web.mjs builds Fabric.Frontend and copies dist -> www;
  npm run sync / apk:debug wire it to Gradle.
- Native android/ project (cap add android) committed; build outputs,
  www/, node_modules, local.properties gitignored.
- Launcher icons = the Fabric mark (adaptive: green mark on black,
  legacy + round) at all densities.

Verified: gradlew assembleDebug -> app-debug.apk (4.2MB) containing
assets/public/index.html + the SPA bundle + Fabric icons.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/variables.gradle

@@ -0,0 +1,16 @@
+ext {
+    minSdkVersion = 23
+    compileSdkVersion = 35
+    targetSdkVersion = 35
+    androidxActivityVersion = '1.9.2'
+    androidxAppCompatVersion = '1.7.0'
+    androidxCoordinatorLayoutVersion = '1.2.0'
+    androidxCoreVersion = '1.15.0'
+    androidxFragmentVersion = '1.8.4'
+    coreSplashScreenVersion = '1.0.1'
+    androidxWebkitVersion = '1.12.1'
+    junitVersion = '4.13.2'
+    androidxJunitVersion = '1.2.1'
+    androidxEspressoCoreVersion = '3.6.1'
+    cordovaAndroidVersion = '10.1.1'
+}