feat: live timer

closes #23

lib/widgets/live_timer.dart

@@ -0,0 +1,49 @@
+import 'dart:async';
+import 'package:flutter/material.dart';
+import 'package:zap_stream_flutter/theme.dart';
+import 'package:zap_stream_flutter/utils.dart';
+import 'package:zap_stream_flutter/widgets/pill.dart';
+
+class LiveTimerWidget extends StatefulWidget {
+  final DateTime started;
+
+  const LiveTimerWidget({super.key, required this.started});
+
+  @override
+  createState() => _LiveTimerWidget();
+}
+
+class _LiveTimerWidget extends State<LiveTimerWidget> {
+  late Timer _timer;
+
+  @override
+  void initState() {
+    super.initState();
+    _timer = Timer.periodic(const Duration(seconds: 1), (timer) {
+      setState(() {
+        // tick
+      });
+    });
+  }
+
+  @override
+  void dispose() {
+    _timer.cancel();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return PillWidget(
+      color: LAYER_2,
+      child: Text(
+        formatSecondsToHHMMSS(
+          ((DateTime.now().millisecondsSinceEpoch -
+                      widget.started.millisecondsSinceEpoch) /
+                  1000)
+              .toInt(),
+        ),
+      ),
+    );
+  }
+}