feat(ground-suite): add replay observability console

ground-suite/lib/core/mavlink/mavlink_byte_source.dart

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+import 'dart:typed_data';
+
+/// Receive-only bytes from one MAVLink transport endpoint.
+///
+/// A source has one reader and owns its close lifecycle. A future adapter will
+/// bind serial, UDP, or a recording source here; no source in the first slice
+/// may write bytes to a vehicle.
+abstract interface class MavlinkByteSource {
+  Stream<Uint8List> get chunks;
+
+  Future<void> close();
+}

ground-suite/lib/core/mavlink/mavlink_event_decoder.dart

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+import '../observations/vehicle_data_update.dart';
+import 'mavlink_byte_source.dart';
+
+/// Converts a receive-only MAVLink byte stream into semantically safe events.
+///
+/// TODO(gcs-live-mavlink): generate this adapter from pinned MAVLink Common
+/// definitions plus Kaptan's `kaptan.xml` root. It must reject MAVLink 1 and
+/// CRC-invalid MAVLink 2 frames, validate every fixed diagnostic length before
+/// UTF-8 decoding, retain unknown enum values and flags, and emit parser or
+/// semantic drop updates without ending the connection.
+abstract interface class MavlinkEventDecoder {
+  Stream<VehicleDataUpdate> decode(MavlinkByteSource source);
+}