feat: add frontend app, improve static file serving with lazy loading and root redirect

frontend/lib/api/client.dart

@@ -0,0 +1,107 @@
+import 'dart:convert';
+import 'package:http/http.dart' as http;
+import 'models.dart';
+
+class APIError implements Exception {
+  final int statusCode;
+  final String message;
+  APIError(this.statusCode, this.message);
+  @override
+  String toString() => 'APIError $statusCode: $message';
+}
+
+class APIClient {
+  final String baseUrl;
+
+  APIClient({this.baseUrl = 'http://localhost:8000'});
+
+  String _url(String path) => '$baseUrl$path';
+
+  static dynamic _decodeBody(http.Response response) {
+    return jsonDecode(response.body);
+  }
+
+  static Map<String, dynamic>? _asMap(dynamic d) {
+    if (d is Map<String, dynamic>) return d;
+    if (d is Map) return d.cast<String, dynamic>();
+    return null;
+  }
+
+  static void _checkError(http.Response response) {
+    if (response.statusCode >= 400) {
+      final body = _decodeBody(response);
+      final map = _asMap(body) ?? {};
+      throw APIError(
+        response.statusCode,
+        map['error'] as String? ?? 'Request failed',
+      );
+    }
+  }
+
+  Future<List<Pipeline>> listPipelines() async {
+    final res = await http.get(Uri.parse(_url('/api/pipelines')));
+    _checkError(res);
+    final data = _decodeBody(res);
+    final arr = data is List ? data : [];
+    final result = <Pipeline>[];
+    for (final e in arr) {
+      final m = _asMap(e);
+      if (m != null) result.add(Pipeline.fromJson(m));
+    }
+    return result;
+  }
+
+  Future<Pipeline> getPipeline(String id) async {
+    final res = await http.get(Uri.parse(_url('/api/pipelines/$id')));
+    _checkError(res);
+    final data = _decodeBody(res);
+    final map = _asMap(data) ?? {};
+    final inner = _asMap(map['data']) ?? map;
+    return Pipeline.fromJson(inner);
+  }
+
+  Future<Pipeline> createPipeline(Pipeline pipeline) async {
+    final res = await http.post(
+      Uri.parse(_url('/api/pipelines')),
+      headers: {'Content-Type': 'application/json'},
+      body: jsonEncode(pipeline.toJson()),
+    );
+    _checkError(res);
+    final data = _decodeBody(res);
+    final map = _asMap(data) ?? {};
+    final inner = _asMap(map['data']) ?? map;
+    return Pipeline.fromJson(inner);
+  }
+
+  Future<void> deletePipeline(String id) async {
+    final res = await http.delete(Uri.parse(_url('/api/pipelines/$id')));
+    _checkError(res);
+  }
+
+  Future<Map<String, dynamic>> startRun(String pipelineId) async {
+    final res = await http.post(
+      Uri.parse(_url('/api/runs')),
+      headers: {'Content-Type': 'application/json'},
+      body: jsonEncode({'pipeline_id': pipelineId}),
+    );
+    _checkError(res);
+    final data = _decodeBody(res);
+    final map = _asMap(data) ?? {};
+    return _asMap(map['data']) ?? map;
+  }
+
+  Future<RunState> getRunStatus(String runId) async {
+    final res = await http.get(Uri.parse(_url('/api/runs/$runId/status')));
+    _checkError(res);
+    final data = _decodeBody(res);
+    final map = _asMap(data) ?? {};
+    final inner = _asMap(map['data']) ?? map;
+    return RunState.fromJson(inner);
+  }
+
+  Future<String> getRunLog(String runId) async {
+    final res = await http.get(Uri.parse(_url('/api/runs/$runId/log')));
+    _checkError(res);
+    return res.body;
+  }
+}