feat(教学): 扩展教学建议链路以支持候选牌列表

扩展教学建议链路，在 PrivateTeachingMessage 中增加 candidates 字段，支持前端展示候选牌、评分和原因标签。同时优化前端组件结构，抽离共享类型和工具函数，为后续页面拆分做准备。

- 后端：在 GameSessionService 和 GameMessagePublisher 中透传候选牌列表
- 前端：新增 GameMessageStack 组件展示教学候选，优化手牌区推荐牌高亮
- 测试：补充 GameMessagePublisherTest 验证候选牌消息结构
- 文档：更新 DEVELOPMENT_PLAN 和 H5_GAME_PAGE_ARCHITECTURE 说明当前前端结构

backend/src/main/java/com/xuezhanmaster/game/service/GameSessionService.java

@@ -301,7 +301,8 @@ public class GameSessionService {
                 currentSeat.getPlayerId(),
                 advice.teachingMode(),
                 advice.recommendedAction(),
-                advice.explanation()
+                advice.explanation(),
+                advice.candidates()
         );
     }
 

backend/src/main/java/com/xuezhanmaster/ws/dto/PrivateTeachingMessage.java

@@ -1,11 +1,15 @@
 package com.xuezhanmaster.ws.dto;
 
+import com.xuezhanmaster.teaching.dto.CandidateAdviceItem;
+
+import java.util.List;
+
 public record PrivateTeachingMessage(
         String gameId,
         String userId,
         String teachingMode,
         String recommendedAction,
-        String explanation
+        String explanation,
+        List<CandidateAdviceItem> candidates
 ) {
 }
-

backend/src/main/java/com/xuezhanmaster/ws/service/GameMessagePublisher.java

@@ -3,6 +3,7 @@ package com.xuezhanmaster.ws.service;
 import com.xuezhanmaster.game.domain.ResponseActionSeatCandidate;
 import com.xuezhanmaster.game.domain.ResponseActionWindow;
 import com.xuezhanmaster.game.event.GameEvent;
+import com.xuezhanmaster.teaching.dto.CandidateAdviceItem;
 import com.xuezhanmaster.ws.dto.PrivateActionCandidate;
 import com.xuezhanmaster.ws.dto.PrivateActionMessage;
 import com.xuezhanmaster.ws.dto.PrivateTeachingMessage;
@@ -97,10 +98,18 @@ public class GameMessagePublisher {
         );
     }
 
-    public void publishPrivateTeaching(String gameId, String userId, String teachingMode, String recommendedAction, String explanation) {
+    public void publishPrivateTeaching(
+            String gameId,
+            String userId,
+            String teachingMode,
+            String recommendedAction,
+            String explanation,
+            List<CandidateAdviceItem> candidates
+    ) {
         messagingTemplate.convertAndSend(
                 "/topic/users/" + userId + "/teaching",
-                new PrivateTeachingMessage(gameId, userId, teachingMode, recommendedAction, explanation)
+                // 教学消息需要同时携带推荐结果与备选列表，前端才能把“为什么是这张牌”解释完整。
+                new PrivateTeachingMessage(gameId, userId, teachingMode, recommendedAction, explanation, candidates)
         );
     }