feat(waiter): Capacitor 8 Android project, native build mode, signed APK tooling

- capacitor.config.json: appId gr.bonamin.xenia, webDir dist-native,
  androidScheme http (origin http://localhost - no mixed-content block when
  calling venue servers over plain HTTP on the LAN)
- vite: `--mode native` builds to dist-native with the PWA plugin disabled
  (no service worker inside the app)
- Android: minSdk 24 / target 36; CAMERA permission for QR pairing;
  cleartext allowed via network_security_config (LAN IPs can't be listed
  per-domain); allowBackup=false so backups never carry login tokens
- Release signing reads ~/.xenia/keystore.properties (override with
  XENIA_KEYSTORE_PROPS) - the key never enters the repo; versionName 1.0.0 /
  versionCode 1 with a bump-both rule for sideloaded updates
- npm scripts build:native, apk:debug, apk:release (scripts/build-apk.mjs);
  APKs land in releases/ (gitignored); release APK is also copied to
  public/downloads/ so venue servers serve it at /downloads/xenia-waiter.apk
- waiter nginx: /downloads/ served as application/vnd.android.package-archive,
  real 404 when missing (never falls through to index.html)
- launcher icons + splash generated from the app icon (assets/ is the source)
- .gitattributes: gradlew LF, *.bat CRLF

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

waiter_pwa/android/app/.gitignore

@@ -0,0 +1,2 @@
+/build/*
+!/build/.npmkeep