Add app source and tests

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

lib/Peach/about/external/data/Health.dart

@@ -0,0 +1,10 @@
+enum HealthStatus { healthy, unhealthy, unknown, disabled, checking }
+
+class HealthResult {
+  final HealthStatus status;
+  final String detail;
+  final DateTime time;
+  HealthResult(this.status, this.detail) : time = DateTime.now();
+
+  static HealthResult checking() => HealthResult(HealthStatus.checking, '…');
+}