feat: Disable system screenshots in recents screen (#608)

This change prevents the app's content from being visible in the recents screen on Android 13 (Tiramisu) and newer devices.

It achieves this by calling `setRecentsScreenshotEnabled(false)` in the `onCreate` method of `MainActivity` after checking the device's SDK version. This enhances user privacy by hiding potentially sensitive information from the system's app overview.

app/src/main/java/com/bitchat/android/MainActivity.kt

@@ -1,6 +1,7 @@
 package com.bitchat.android
 
 import android.content.Intent
+import android.os.Build
 import android.os.Bundle
 import android.util.Log
 import androidx.activity.OnBackPressedCallback
@@ -80,7 +81,9 @@ class MainActivity : OrientationAwareActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
-        
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
+            this.setRecentsScreenshotEnabled(false)
+        }
         // Register receiver for force finish signal from shutdown coordinator
         val filter = android.content.IntentFilter(com.bitchat.android.util.AppConstants.UI.ACTION_FORCE_FINISH)
         if (android.os.Build.VERSION.SDK_INT >= 33) {