feat(watch): phone session projection to watch (#91-B)

lib/application/watch_companion_use_cases.dart

@@ -0,0 +1,20 @@
+import 'package:watch_bridge_contract/watch_bridge_contract.dart';
+
+abstract interface class WatchCommandIngress {
+  Future<WatchCommandAck> dispatch(WatchCommandEnvelope command);
+}
+
+abstract interface class WatchProjectionPublisher {
+  Future<void> publish(WatchSessionProjection projection);
+}
+
+abstract interface class WatchProjectionSource {
+  Stream<WatchSessionProjection> get projections;
+
+  Future<WatchSessionProjection> currentProjection();
+
+  Future<WatchSessionProjection> emitCurrentProjection();
+}
+
+abstract interface class WatchCompanionUseCases
+    implements WatchCommandIngress, WatchProjectionSource {}