new: add loading overlay for WebView widget while pages load

shared/src/jvmMain/kotlin/bzh/ajaury/chombev/web/ui/PlatformWebView.jvm.kt

@@ -1,14 +1,17 @@
 package bzh.ajaury.chombev.web.ui
 
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.ui.Modifier
 
 @Composable
 actual fun PlatformWebView(
     url: String,
     darkTheme: Boolean,
+    onLoadingStateChange: (Boolean) -> Unit,
     modifier: Modifier,
 ) {
-    // Desktop has no bundled web view; offer to open the page in the system browser instead.
+    // Desktop has no bundled web view; nothing loads, so report done and offer the system browser.
+    LaunchedEffect(Unit) { onLoadingStateChange(false) }
     WebViewUnavailable(url = url, modifier = modifier)
 }