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/settings.gradle

@@ -0,0 +1,16 @@
+pluginManagement {
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+rootProject.name = "Pantree"
+include ':app'