feat(shared): add InAppBrowser widget for modal web page display

- Implement InAppBrowser as a modal widget using InAppWebView
- Include custom app bar with close button and progress indicator
- Restrict navigation to initial domain to maintain focus
- Add show method for easy presentation as a modal dialog

Author: fulleni

lib/shared/widgets/in_app_browser.dart

@@ -0,0 +1,77 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_inappwebview/flutter_inappwebview.dart';
+
+/// {@template in_app_browser}
+/// A modal widget that displays a web page within the app using a custom
+/// InAppWebView implementation.
+///
+/// This browser is presented modally and includes a custom app bar with a
+/// close button, providing a consistent and controlled browsing experience.
+/// {@endtemplate}
+class InAppBrowser extends StatefulWidget {
+  /// {@macro in_app_browser}
+  const InAppBrowser({required this.url, super.key});
+
+  /// The initial URL to load in the web view.
+  final String url;
+
+  /// A static method to show the browser as a modal dialog.
+  static Future<void> show(BuildContext context, {required String url}) {
+    return showGeneralDialog(
+      context: context,
+      barrierDismissible: false,
+      pageBuilder: (context, animation, secondaryAnimation) =>
+          InAppBrowser(url: url),
+    );
+  }
+
+  @override
+  State<InAppBrowser> createState() => _InAppBrowserState();
+}
+
+class _InAppBrowserState extends State<InAppBrowser> {
+  double _progress = 0;
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+
+    return Scaffold(
+      appBar: AppBar(
+        leading: IconButton(
+          icon: const Icon(Icons.close),
+          onPressed: () => Navigator.of(context).pop(),
+        ),
+        backgroundColor: theme.colorScheme.surface,
+        elevation: 0,
+        bottom: _progress < 1.0
+            ? PreferredSize(
+                preferredSize: const Size.fromHeight(2),
+                child: LinearProgressIndicator(
+                  value: _progress,
+                  backgroundColor: Colors.transparent,
+                ),
+              )
+            : null,
+      ),
+      body: InAppWebView(
+        initialUrlRequest: URLRequest(url: WebUri(widget.url)),
+        initialSettings: InAppWebViewSettings(
+          // Restrict navigation to the initial domain to keep the user focused.
+          useShouldOverrideUrlLoading: true,
+        ),
+        onProgressChanged: (controller, progress) {
+          setState(() {
+            _progress = progress / 100;
+          });
+        },
+        shouldOverrideUrlLoading: (controller, navigationAction) async {
+          // Allow the initial URL to load, but cancel any subsequent navigations.
+          return navigationAction.isForMainFrame
+              ? NavigationActionPolicy.CANCEL
+              : NavigationActionPolicy.ALLOW;
+        },
+      ),
+    );
+  }
+}