feat(android): implement auth screens, onboarding flow, and account setup

- Add AuthRepository with EncryptedSharedPreferences and OkHttp API calls
- Add AuthViewModel with login/signup/reset/Google Sign-In flows
- Create auth screens: AuthScreen, LoginScreen, SignupScreen,
  ForgotPasswordScreen, ResetPasswordScreen, BiometricAuthScreen
- Create onboarding screens with HorizontalPager: PlanSelection,
  WatchlistSetup, FamilyInvite, Complete (with checkmark animation)
- Wire auth state to navigation: unauthenticated→auth, new→onboarding,
  authenticated→dashboard
- Add PasswordStrength utility with tests
- Add dependencies: security-crypto, biometric, play-services-auth,
  okhttp, gson, lottie-compose, material-icons-core
- Add unit tests: 23 tests passing for AuthViewModel and PasswordStrength

android/ShieldAI/app/build.gradle.kts

@@ -50,8 +50,16 @@ dependencies {
     implementation(libs.androidx.compose.ui.tooling.preview)
     implementation(libs.androidx.compose.material3)
     implementation(libs.androidx.compose.material3.adaptive.navigation.suite)
+    implementation("androidx.compose.material:material-icons-core")
     implementation(libs.coil.compose)
+    implementation(libs.androidx.security.crypto)
+    implementation(libs.androidx.biometric)
+    implementation(libs.play.services.auth)
+    implementation(libs.okhttp)
+    implementation(libs.gson)
+    implementation(libs.lottie.compose)
     testImplementation(libs.junit)
+    testImplementation(libs.kotlinx.coroutines.test)
     androidTestImplementation(libs.androidx.junit)
     androidTestImplementation(libs.androidx.espresso.core)
     androidTestImplementation(platform(libs.androidx.compose.bom))