Progress on basic UI for testing

lib/pages/add_app.dart

@@ -0,0 +1,72 @@
+import 'package:flutter/material.dart';
+import 'package:obtainium/pages/app.dart';
+import 'package:obtainium/services/apps_provider.dart';
+import 'package:obtainium/services/source_service.dart';
+import 'package:provider/provider.dart';
+
+class AddAppPage extends StatefulWidget {
+  const AddAppPage({super.key});
+
+  @override
+  State<AddAppPage> createState() => _AddAppPageState();
+}
+
+class _AddAppPageState extends State<AddAppPage> {
+  final _formKey = GlobalKey<FormState>();
+  final urlInputController = TextEditingController();
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Obtainium - Add App'),
+      ),
+      body: Center(
+          child: Form(
+        key: _formKey,
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            TextFormField(
+              controller: urlInputController,
+              validator: (value) {
+                if (value == null ||
+                    value.isEmpty ||
+                    Uri.tryParse(value) == null) {
+                  return 'Please enter a supported source URL';
+                }
+                return null;
+              },
+            ),
+            Padding(
+              padding: const EdgeInsets.symmetric(vertical: 16.0),
+              child: ElevatedButton(
+                onPressed: () {
+                  if (_formKey.currentState!.validate()) {
+                    SourceService()
+                        .getApp(urlInputController.value.text)
+                        .then((app) {
+                      var appsProvider = context.read<AppsProvider>();
+                      appsProvider.saveApp(app).then((_) {
+                        Navigator.push(
+                            context,
+                            MaterialPageRoute(
+                                builder: (context) => AppPage(appId: app.id)));
+                      });
+                    }).catchError((e) {
+                      ScaffoldMessenger.of(context).showSnackBar(
+                        SnackBar(content: Text(e.toString())),
+                      );
+                    });
+                  }
+                },
+                child: const Text('Add'),
+              ),
+            ),
+          ],
+        ),
+      )),
+    );
+  }
+}