feat: add splash screen and login auth flow

app/src/main/AndroidManifest.xml

@@ -1,15 +1,22 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
 
+    <uses-permission android:name="android.permission.INTERNET" />
+
     <application
         android:allowBackup="true"
         android:dataExtractionRules="@xml/data_extraction_rules"
         android:fullBackupContent="@xml/backup_rules"
         android:label="@string/app_name"
         android:supportsRtl="true"
+        android:usesCleartextTraffic="true"
         android:theme="@style/Theme.Kanbn4Droid">
+        <activity
+            android:name=".BoardsPlaceholderActivity"
+            android:exported="false" />
         <activity
             android:name=".MainActivity"
+            android:theme="@style/Theme.Kanbn4Droid.Splash"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />