feat(ping): add Ping.ts with PingType and PingPlacedEvent definitions

src/core/game/Ping.ts

@@ -0,0 +1,17 @@
+import { TileRef } from "./GameMap";
+
+export enum PingType {
+  Attack,
+  Retreat,
+  Defend,
+  WatchOut,
+}
+
+export class Ping {
+  constructor(
+    public type: PingType,
+    public tile: TileRef,
+  ) {}
+}
+
+export class PingPlacedEvent extends Ping {}