Add web HTTP-FLV playback path

frontend/lib/widgets/web_stream_player_web.dart

@@ -0,0 +1,38 @@
+import 'dart:html' as html;
+import 'dart:ui_web' as ui_web;
+
+import 'package:flutter/material.dart';
+
+class WebStreamPlayer extends StatefulWidget {
+  final String streamUrl;
+
+  const WebStreamPlayer({super.key, required this.streamUrl});
+
+  @override
+  State<WebStreamPlayer> createState() => _WebStreamPlayerState();
+}
+
+class _WebStreamPlayerState extends State<WebStreamPlayer> {
+  late final String _viewType;
+
+  @override
+  void initState() {
+    super.initState();
+    _viewType = 'flv-player-${DateTime.now().microsecondsSinceEpoch}';
+
+    ui_web.platformViewRegistry.registerViewFactory(_viewType, (int viewId) {
+      final iframe = html.IFrameElement()
+        ..src = 'flv_player.html?src=${Uri.encodeComponent(widget.streamUrl)}'
+        ..style.border = '0'
+        ..style.width = '100%'
+        ..style.height = '100%'
+        ..allow = 'autoplay; fullscreen';
+      return iframe;
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return HtmlElementView(viewType: _viewType);
+  }
+}