feat: 实现响应候选模型与私有动作消息结构化

新增响应候选领域模型和结构化私有动作消息，支持响应窗口和候选动作下发。主要变更包括：

- 新增 ResponseActionOption、ResponseActionSeatCandidate 和 ResponseActionWindow 模型
- 扩展 PrivateActionMessage 支持响应候选上下文
- 实现 ResponseActionWindowBuilder 构建弃牌响应候选
- 拆分 GameMessagePublisher 支持回合动作和响应动作消息
- 更新前端原型页展示结构化候选动作
- 新增响应优先级规则文档 RESPONSE_RESOLUTION_RULES.md

backend/src/main/java/com/xuezhanmaster/game/domain/GameSession.java

@@ -4,7 +4,9 @@ import com.xuezhanmaster.game.event.GameEvent;
 
 import java.util.ArrayList;
 import java.time.Instant;
+import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.UUID;
 
 public class GameSession {
@@ -14,6 +16,8 @@ public class GameSession {
     private final Instant createdAt;
     private final GameTable table;
     private final List<GameEvent> events;
+    private ResponseActionWindow pendingResponseActionWindow;
+    private final Map<Integer, ActionType> responseActionSelections;
 
     public GameSession(String roomId, GameTable table) {
         this.gameId = UUID.randomUUID().toString();
@@ -21,6 +25,7 @@ public class GameSession {
         this.createdAt = Instant.now();
         this.table = table;
         this.events = new ArrayList<>();
+        this.responseActionSelections = new LinkedHashMap<>();
     }
 
     public String getGameId() {
@@ -42,4 +47,20 @@ public class GameSession {
     public List<GameEvent> getEvents() {
         return events;
     }
+
+    public ResponseActionWindow getPendingResponseActionWindow() {
+        return pendingResponseActionWindow;
+    }
+
+    public void setPendingResponseActionWindow(ResponseActionWindow pendingResponseActionWindow) {
+        this.pendingResponseActionWindow = pendingResponseActionWindow;
+    }
+
+    public Map<Integer, ActionType> getResponseActionSelections() {
+        return responseActionSelections;
+    }
+
+    public void clearResponseActionSelections() {
+        responseActionSelections.clear();
+    }
 }