feat: login key / create account

closes #4

lib/pages/login_input.dart

@@ -0,0 +1,56 @@
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+import 'package:ndk/shared/nips/nip19/nip19.dart';
+import 'package:zap_stream_flutter/login.dart';
+import 'package:zap_stream_flutter/main.dart';
+import 'package:zap_stream_flutter/theme.dart';
+import 'package:zap_stream_flutter/widgets/button.dart';
+
+class LoginInputPage extends StatefulWidget {
+  const LoginInputPage({super.key});
+
+  @override
+  State<StatefulWidget> createState() => _LoginInputPage();
+}
+
+class _LoginInputPage extends State<LoginInputPage> {
+  final TextEditingController _controller = TextEditingController();
+  String? _error;
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      spacing: 20,
+      children: [
+        TextFormField(
+          controller: _controller,
+          decoration: InputDecoration(labelText: "npub/nsec"),
+        ),
+        BasicButton.text(
+          "Login",
+          onTap: () async {
+            try {
+              final keyData = Nip19.decode(_controller.text);
+              if (keyData.isNotEmpty) {
+                loginData.value = LoginAccount.nip19(_controller.text);
+                context.go("/");
+              } else {
+                throw "Invalid key";
+              }
+            } catch (e) {
+              setState(() {
+                _error = e.toString();
+              });
+            }
+          },
+        ),
+
+        if (_error != null)
+          Text(
+            _error!,
+            style: TextStyle(color: WARNING, fontWeight: FontWeight.bold),
+          ),
+      ],
+    );
+  }
+}