fix: request install-packages permission at runtime before APK install

Android 8+ requires canRequestPackageInstalls() to return true even when
REQUEST_INSTALL_PACKAGES is declared in the manifest. Add permission_handler
and check/request Permission.requestInstallPackages before downloading;
redirects user to Settings if not granted and shows a clear error message.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/providers/update_provider.dart

@@ -3,6 +3,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:open_file/open_file.dart';
 import 'package:package_info_plus/package_info_plus.dart';
 import 'package:path_provider/path_provider.dart';
+import 'package:permission_handler/permission_handler.dart';
 
 enum UpdateStatus { idle, checking, available, downloading, upToDate, error }
 
@@ -102,6 +103,22 @@ class UpdateNotifier extends Notifier<UpdateState> {
 
   Future<void> downloadAndInstall() async {
     if (state.downloadUrl == null) return;
+
+    // Android 8+ requires explicit per-app "Install unknown apps" approval
+    // beyond the manifest declaration. Check and redirect to Settings if needed.
+    final installPermission = await Permission.requestInstallPackages.status;
+    if (!installPermission.isGranted) {
+      final result = await Permission.requestInstallPackages.request();
+      if (!result.isGranted) {
+        state = state.copyWith(
+          status: UpdateStatus.error,
+          errorMessage:
+              'Grant "Install unknown apps" permission for Fabled in Settings, then try again.',
+        );
+        return;
+      }
+    }
+
     state = state.copyWith(status: UpdateStatus.downloading, downloadProgress: 0);
 
     try {

pubspec.yaml

@@ -22,6 +22,7 @@ dependencies:
   markdown: ^7.2.2
   package_info_plus: ^9.0.0
   open_file: ^3.3.2
+  permission_handler: ^11.3.1
   flutter_inappwebview: ^6.1.5
   flutter_markdown_plus: ^1.0.7
   google_fonts: ^8.0.2