Implemented network-based authentication and secure token storage

- Replaced mock login logic in `LoginViewModel` with actual API calls using Retrofit.
- Integrated `EncryptedSharedPreferences` via a new `TokenStorage` class to securely persist access and refresh tokens.
- Added `RetrofitProvider` and `APIService` to handle network requests and JSON serialization.
- Updated `Account` entity and database schema (version 2) to include user roles, enabling destructive migration for development.
- Added necessary internet permissions and allowed cleartext traffic in `AndroidManifest.xml`.
- Included dependencies for Retrofit, OkHttp logging, and AndroidX Security.

app/build.gradle.kts

@@ -65,4 +65,12 @@ dependencies {
     val room_version = "2.8.4"
     implementation("androidx.room:room-runtime:$room_version")
     ksp("androidx.room:room-compiler:$room_version")
+
+    // Retrofit + Gson
+    implementation("com.squareup.retrofit2:retrofit:2.9.0")
+    implementation("com.squareup.retrofit2:converter-gson:2.9.0")
+    // OkHttp logging (debug)
+    implementation("com.squareup.okhttp3:logging-interceptor:4.9.3")
+    // AndroidX Security (EncryptedSharedPreferences)
+    implementation("androidx.security:security-crypto:1.1.0-alpha03")
 }