chore: replace HTML error pages with native UI and implement safe-area insets

- Delete static HTML error assets and `error.css`.
- Implement native `isError` state and Compose-based loading/error overlays in `MainActivity`.
- Update `SecureWebViewClient` to trigger the `isError` state on request failures.
- Inject JavaScript in `onPageFinished` to dynamically adjust web content for safe-area insets (top and bottom).
- Update `WebApppTheme` to use transparent status and navigation bars with dynamic icon coloring.
- Bump version to 1.2 in `build.gradle.kts`.
- Refactor `WebViewScreen` and `SecureWebViewClient` to handle the new error state.

Author: mrepol742

.idea/deploymentTargetSelector.xml

@@ -52,7 +52,7 @@ android {
         targetSdk = 36
 
         versionCode = dateVersionCode
-        versionName = "1.1 ($dateVersionCode)"
+        versionName = "1.2 ($dateVersionCode)"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
         vectorDrawables {