feat: 안드로이드 하이브리드 앱(Capacitor) 구성

- capacitor.config + android/ 네이티브 프로젝트
- 앱 전용 빌드(.env.capacitor, build:app), 뒤로가기·safe-area
- docs/ANDROID.md

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

android/app/src/main/res/values/ic_launcher_background.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="ic_launcher_background">#FFFFFF</color>
+</resources>

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

@@ -0,0 +1,7 @@
+<?xml version='1.0' encoding='utf-8'?>
+<resources>
+    <string name="app_name">Slim Budget</string>
+    <string name="title_activity_main">Slim Budget</string>
+    <string name="package_name">kr.sblog.slimbudget</string>
+    <string name="custom_url_scheme">kr.sblog.slimbudget</string>
+</resources>

android/app/src/main/res/values/styles.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <!-- Base application theme. -->
+    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
+        <!-- Customize your theme here. -->
+        <item name="colorPrimary">@color/colorPrimary</item>
+        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
+        <item name="colorAccent">@color/colorAccent</item>
+    </style>
+
+    <style name="AppTheme.NoActionBar" parent="Theme.AppCompat.DayNight.NoActionBar">
+        <item name="windowActionBar">false</item>
+        <item name="windowNoTitle">true</item>
+        <item name="android:background">@null</item>
+    </style>
+
+
+    <style name="AppTheme.NoActionBarLaunch" parent="Theme.SplashScreen">
+        <item name="android:background">@drawable/splash</item>
+    </style>
+</resources>