feat(android): scaffold Capacitor 8 native project + hardware Back button

Add @capacitor/{core,android,app,cli,assets} to ui/, a capacitor.config.ts (appId ru.eruditgame.app, appName Эрудит, webDir dist — bundle model, no server.url), and the generated ui/android/ Gradle project (tracked; build outputs and the machine-specific local.properties gitignored, keystore patterns un-commented so signing material can never be committed). Wire the Android hardware Back button in ui/src/lib/native.ts behind a dynamic @capacitor/app import (web/mock bundles never load it), called from App.svelte onMount and reusing routeDepth for the navigation-root check. Whitelist sharp in pnpm-workspace.yaml for @capacitor/assets icon generation.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ui/android/.gitignore

@@ -0,0 +1,101 @@
+# Using Android gitignore template: https://github.com/github/gitignore/blob/HEAD/Android.gitignore
+
+# Built application files
+*.apk
+*.aar
+*.ap_
+*.aab
+
+# Files for the ART/Dalvik VM
+*.dex
+
+# Java class files
+*.class
+
+# Generated files
+bin/
+gen/
+out/
+#  Uncomment the following line in case you need and you don't have the release build type files in your app
+# release/
+
+# Gradle files
+.gradle/
+build/
+
+# Local configuration file (sdk path, etc)
+local.properties
+
+# Proguard folder generated by Eclipse
+proguard/
+
+# Log Files
+*.log
+
+# Android Studio Navigation editor temp files
+.navigation/
+
+# Android Studio captures folder
+captures/
+
+# IntelliJ
+*.iml
+.idea/workspace.xml
+.idea/tasks.xml
+.idea/gradle.xml
+.idea/assetWizardSettings.xml
+.idea/dictionaries
+.idea/libraries
+# Android Studio 3 in .gitignore file.
+.idea/caches
+.idea/modules.xml
+# Comment next line if keeping position of elements in Navigation Editor is relevant for you
+.idea/navEditor.xml
+
+# Keystore files
+# Release signing material must never be committed (see ANDROID_PLAN.md — keystore loss/leak risk).
+*.jks
+*.keystore
+
+# External native build folder generated in Android Studio 2.2 and later
+.externalNativeBuild
+.cxx/
+
+# Google Services (e.g. APIs or Firebase)
+# google-services.json
+
+# Freeline
+freeline.py
+freeline/
+freeline_project_description.json
+
+# fastlane
+fastlane/report.xml
+fastlane/Preview.html
+fastlane/screenshots
+fastlane/test_output
+fastlane/readme.md
+
+# Version control
+vcs.xml
+
+# lint
+lint/intermediates/
+lint/generated/
+lint/outputs/
+lint/tmp/
+# lint/reports/
+
+# Android Profiling
+*.hprof
+
+# Cordova plugins for Capacitor
+capacitor-cordova-android-plugins
+
+# Copied web assets
+app/src/main/assets/public
+
+# Generated Config files
+app/src/main/assets/capacitor.config.json
+app/src/main/assets/capacitor.plugins.json
+app/src/main/res/xml/config.xml