feat(android): implement full Android frontend

- Build config: build.gradle (app + root), settings.gradle, AndroidManifest
- Application entry: PantreeApplication (Hilt), MainActivity (Compose host)
- Data layer:
  - ApiService (Retrofit interface, all 20 endpoints)
  - ApiModels (all request/response DTOs)
  - AuthInterceptor (JWT Bearer header injection)
  - TokenStore (EncryptedSharedPreferences)
  - SyncPreferences (DataStore, last-sync timestamp)
  - PantreeDatabase (Room, 5 entities)
  - Entities: PantryItemEntity, RecipeEntity, RecipeIngredientEntity, ShoppingListEntity, ShoppingListItemEntity
  - DAOs: PantryDao, RecipeDao, ShoppingListDao
  - Repositories: AuthRepository, PantryRepository, RecipeRepository, ShoppingListRepository, SyncRepository
- DI: AppModule (Hilt, provides OkHttp/Retrofit/Room/DAOs)
- Util: Result<T> sealed class, safeApiCall, toUserMessage (human-readable error mapping)
- Sync: SyncManager (DefaultLifecycleObserver, triggers on app open/foreground)
- Theme: Color, Type, Theme (Material 3, light + dark)
- Navigation: Screen sealed class, PantreeNavGraph (deep links for password reset)
- Shared components: LoadingState, ErrorState, EmptyState, OfflineBanner, PantreeTopBar
- Auth screens: SplashScreen, SignInScreen, SignUpScreen, ForgotPasswordScreen, ResetPasswordScreen + AuthViewModel
- Pantry screen: PantryScreen (list/add/edit/delete dialogs) + PantryViewModel
- Recipe screens: RecipesScreen (filter chips, search, availability badges) + RecipeDetailScreen (scale 1x/2x/3x, ingredient pantry status) + RecipeViewModel
- Shopping screens: ShoppingListsScreen + ShoppingListDetailScreen (check-off, progress bar, merge feedback, add-from-recipes) + ShoppingListViewModel
- Settings screen: sign out + account deletion (15-day window copy) + SettingsViewModel
- Tests: ResultTest (unit), RecipeDetailScreenTest (unit), PantryScreenTest (instrumented)
- README: architecture, module structure, UI states table, sync strategy, setup

Every screen handles loading / error / empty / success states.
Offline: cached Room data shown read-only.

android/app/build.gradle

@@ -0,0 +1,128 @@
+plugins {
+    id 'com.android.application'
+    id 'org.jetbrains.kotlin.android'
+    id 'com.google.dagger.hilt.android'
+    id 'com.google.devtools.ksp'
+}
+
+android {
+    namespace 'com.pantree.app'
+    compileSdk 34
+
+    defaultConfig {
+        applicationId "com.pantree.app"
+        minSdk 26
+        targetSdk 34
+        versionCode 1
+        versionName "1.0.0"
+
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+        vectorDrawables {
+            useSupportLibrary true
+        }
+
+        buildConfigField "String", "BASE_URL", '"https://api.pantree.app/v1/"'
+        buildConfigField "String", "GOOGLE_WEB_CLIENT_ID", '"YOUR_GOOGLE_WEB_CLIENT_ID"'
+    }
+
+    buildTypes {
+        release {
+            minifyEnabled true
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+        }
+        debug {
+            buildConfigField "String", "BASE_URL", '"http://10.0.2.2:3000/v1/"'
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_17
+        targetCompatibility JavaVersion.VERSION_17
+    }
+
+    kotlinOptions {
+        jvmTarget = '17'
+    }
+
+    buildFeatures {
+        compose true
+        buildConfig true
+    }
+
+    composeOptions {
+        kotlinCompilerExtensionVersion '1.5.11'
+    }
+
+    packaging {
+        resources {
+            excludes += '/META-INF/{AL2.0,LGPL2.1}'
+        }
+    }
+}
+
+dependencies {
+    // Core
+    implementation 'androidx.core:core-ktx:1.13.0'
+    implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.7.0'
+    implementation 'androidx.activity:activity-compose:1.9.0'
+
+    // Compose BOM
+    implementation platform('androidx.compose:compose-bom:2024.04.01')
+    implementation 'androidx.compose.ui:ui'
+    implementation 'androidx.compose.ui:ui-graphics'
+    implementation 'androidx.compose.ui:ui-tooling-preview'
+    implementation 'androidx.compose.material3:material3'
+    implementation 'androidx.compose.material:material-icons-extended'
+
+    // Navigation
+    implementation 'androidx.navigation:navigation-compose:2.7.7'
+
+    // Hilt DI
+    implementation 'com.google.dagger:hilt-android:2.51.1'
+    ksp 'com.google.dagger:hilt-android-compiler:2.51.1'
+    implementation 'androidx.hilt:hilt-navigation-compose:1.2.0'
+
+    // Room
+    implementation 'androidx.room:room-runtime:2.6.1'
+    implementation 'androidx.room:room-ktx:2.6.1'
+    ksp 'androidx.room:room-compiler:2.6.1'
+
+    // Retrofit + OkHttp
+    implementation 'com.squareup.retrofit2:retrofit:2.11.0'
+    implementation 'com.squareup.retrofit2:converter-gson:2.11.0'
+    implementation 'com.squareup.okhttp3:okhttp:4.12.0'
+    implementation 'com.squareup.okhttp3:logging-interceptor:4.12.0'
+
+    // Gson
+    implementation 'com.google.code.gson:gson:2.10.1'
+
+    // ViewModel + StateFlow
+    implementation 'androidx.lifecycle:lifecycle-viewmodel-compose:2.7.0'
+    implementation 'androidx.lifecycle:lifecycle-runtime-compose:2.7.0'
+
+    // EncryptedSharedPreferences
+    implementation 'androidx.security:security-crypto:1.1.0-alpha06'
+
+    // Google Identity (One Tap)
+    implementation 'com.google.android.gms:play-services-auth:21.1.1'
+
+    // Coil (image loading)
+    implementation 'io.coil-kt:coil-compose:2.6.0'
+
+    // DataStore
+    implementation 'androidx.datastore:datastore-preferences:1.1.0'
+
+    // Coroutines
+    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.8.0'
+
+    // Testing
+    testImplementation 'junit:junit:4.13.2'
+    testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.8.0'
+    testImplementation 'io.mockk:mockk:1.13.10'
+    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
+    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
+    androidTestImplementation platform('androidx.compose:compose-bom:2024.04.01')
+    androidTestImplementation 'androidx.compose.ui:ui-test-junit4'
+    debugImplementation 'androidx.compose.ui:ui-tooling'
+    debugImplementation 'androidx.compose.ui:ui-test-manifest'
+}