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/ResponseActionWindow.java

@@ -0,0 +1,34 @@
+package com.xuezhanmaster.game.domain;
+
+import java.time.Instant;
+import java.util.List;
+import java.util.UUID;
+
+public record ResponseActionWindow(
+        String windowId,
+        String gameId,
+        String triggerEventType,
+        int sourceSeatNo,
+        String triggerTile,
+        List<ResponseActionSeatCandidate> seatCandidates,
+        Instant createdAt
+) {
+
+    public static ResponseActionWindow create(
+            String gameId,
+            String triggerEventType,
+            int sourceSeatNo,
+            String triggerTile,
+            List<ResponseActionSeatCandidate> seatCandidates
+    ) {
+        return new ResponseActionWindow(
+                UUID.randomUUID().toString(),
+                gameId,
+                triggerEventType,
+                sourceSeatNo,
+                triggerTile,
+                List.copyOf(seatCandidates),
+                Instant.now()
+        );
+    }
+}