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/src/main/AndroidManifest.xml

@@ -2,6 +2,8 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools">
 
+    <uses-permission android:name="android.permission.INTERNET" />
+
     <application
         android:allowBackup="true"
         android:dataExtractionRules="@xml/data_extraction_rules"
@@ -10,6 +12,7 @@
         android:label="@string/app_name"
         android:roundIcon="@mipmap/ic_launcher_round"
         android:supportsRtl="true"
+        android:usesCleartextTraffic="true"
         android:theme="@style/Theme.ShapPlanner">
         <activity
             android:name=".activities.MainActivity"