Keep the system splash until the first real screen: no blank WebView gap, no second splash

Installed APK sequence was system splash -> white WebView -> web splash -> home. The
activity now holds the system splash (core-splashscreen) until the page calls
TadrisinoAndroid.appReady(), after its first non-boot screen; released after 10s or on a
main-frame load error so a dead site shows the WebView error, not an endless splash.
Older APKs have no appReady and are unaffected. Debug build compiles; not run on a device.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -105,5 +105,7 @@ android {
 dependencies {
     implementation("androidx.appcompat:appcompat:1.7.0")
     implementation("androidx.activity:activity-ktx:1.9.2")
+    // اسپلشِ سیستم تا آماده‌شدنِ اولین صفحه‌ی وب می‌ماند (MainActivity.keepSplash).
+    implementation("androidx.core:core-splashscreen:1.0.1")
     implementation("com.github.cafebazaar.Poolakey:poolakey:2.2.0")
 }