Add app source and tests

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

lib/Peach/see/kafka/ConnectKafka.dart

@@ -0,0 +1,36 @@
+import '../../about/external/data/Kafka.dart';
+
+/// One scan's worth of cluster state.
+class KafkaScan {
+  final List<KafkaTopic> topics;
+  final List<KafkaConsumerGroup> groups;
+  final KafkaCluster cluster;
+
+  const KafkaScan({
+    required this.topics,
+    required this.groups,
+    required this.cluster,
+  });
+
+  /// Nothing came back at all — usually an unreachable bootstrap server rather
+  /// than a genuinely empty cluster.
+  bool get isEmpty =>
+      topics.isEmpty && groups.isEmpty && cluster.brokers.isEmpty;
+}
+
+abstract class ConnectKafka {
+  /// Whether the Kafka CLI tools were found, and where.
+  void onKafkaDetected(KafkaStatus status);
+
+  /// Detection itself failed (the server couldn't be probed).
+  void onDetectFailed(String message);
+
+  /// Topics, groups and cluster health, freshly read.
+  void onScanned(KafkaScan scan);
+
+  /// The scan failed.
+  void onScanFailed(String message);
+
+  /// Output of the broker probe, to show in a sheet.
+  void onProbeOutput(String title, String output);
+}