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/app/src/main/res/values/strings.xml

@@ -0,0 +1,7 @@
+<?xml version='1.0' encoding='utf-8'?>
+<resources>
+    <string name="app_name">Эрудит</string>
+    <string name="title_activity_main">Эрудит</string>
+    <string name="package_name">ru.eruditgame.app</string>
+    <string name="custom_url_scheme">ru.eruditgame.app</string>
+</resources>