embargo if attacked (#353)

## Responsibility Acknowledgment

- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through basic manual testing:
  - Significantly slows down the entire development process
  - Blocks releases and new features for all contributors
  - Harms the project's reliability and reputation
- Places additional debugging burden on maintainers who already have
limited time
- Diverts valuable resources away from new development and improvements
  - Makes me seen as a loser
  - Makes me more likely to go to hell

src/core/execution/AttackExecution.ts

@@ -81,6 +81,10 @@ export class AttackExecution implements Execution {
         ? mg.terraNullius()
         : mg.player(this._targetID);
 
+    if (this.target && this.target.isPlayer()) {
+      (this.target as Player).addEmbargo(this._owner.id());
+    }
+
     if (this._owner == this.target) {
       console.error(`Player ${this._owner} cannot attack itself`);
       this.active = false;