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

frontend/src/App.vue

@@ -63,11 +63,22 @@ type PublicGameMessage = {
   createdAt: string
 }
 
+type PrivateActionCandidate = {
+  actionType: string
+  tile: string | null
+}
+
 type PrivateActionMessage = {
   gameId: string
   userId: string
+  actionScope: string
   availableActions: string[]
   currentSeatNo: number
+  windowId: string | null
+  triggerEventType: string | null
+  sourceSeatNo: number | null
+  triggerTile: string | null
+  candidates: PrivateActionCandidate[]
 }
 
 type PrivateTeachingMessage = {
@@ -107,11 +118,24 @@ const phaseLabelMap: Record<string, string> = {
   LACK_SELECTION: '定缺阶段'
 }
 
+const actionScopeLabelMap: Record<string, string> = {
+  TURN: '当前回合动作',
+  RESPONSE: '响应候选动作'
+}
+
 const canSelectLack = computed(() => game.value?.phase === 'LACK_SELECTION')
 const canDiscard = computed(
   () => game.value?.phase === 'PLAYING' && game.value.selfSeat.playerId === currentUserId.value && game.value.currentSeatNo === game.value.selfSeat.seatNo
 )
 const publicSeats = computed(() => game.value?.seats ?? [])
+const privateActionCandidates = computed(() => privateAction.value?.candidates ?? [])
+const privateActionSummary = computed(() => {
+  if (!privateAction.value) {
+    return ''
+  }
+  const scopeLabel = actionScopeLabelMap[privateAction.value.actionScope] ?? privateAction.value.actionScope
+  return `${scopeLabel}：${privateAction.value.availableActions.join(' / ')}`
+})
 
 async function requestJson<T>(url: string, options?: RequestInit): Promise<T> {
   const response = await fetch(url, {
@@ -516,7 +540,27 @@ function discard(tile: string) {
         <div class="message-stack">
           <div class="message-card">
             <span class="meta-label">私有动作消息</span>
-            <strong v-if="privateAction">{{ privateAction.availableActions.join(' / ') }}</strong>
+            <template v-if="privateAction">
+              <strong>{{ privateActionSummary }}</strong>
+              <div class="mini-tags action-meta-row">
+                <span class="mini-tag">座位 {{ privateAction.currentSeatNo }}</span>
+                <span class="mini-tag">{{ actionScopeLabelMap[privateAction.actionScope] ?? privateAction.actionScope }}</span>
+                <span v-if="privateAction.triggerTile" class="mini-tag">目标牌 {{ privateAction.triggerTile }}</span>
+                <span v-if="privateAction.sourceSeatNo !== null" class="mini-tag">来源座位 {{ privateAction.sourceSeatNo }}</span>
+              </div>
+              <div class="candidate-list" v-if="privateActionCandidates.length > 0">
+                <span
+                  v-for="(candidate, index) in privateActionCandidates"
+                  :key="`${candidate.actionType}-${candidate.tile ?? 'none'}-${index}`"
+                  class="candidate-chip"
+                >
+                  {{ candidate.actionType }}<template v-if="candidate.tile"> · {{ candidate.tile }}</template>
+                </span>
+              </div>
+              <span v-if="privateAction.actionScope === 'RESPONSE'" class="message-copy">
+                当前原型页已能识别响应候选消息，后续会继续补正式动作面板和真实响应流程。
+              </span>
+            </template>
             <span v-else class="empty-copy">尚未收到私有动作消息</span>
           </div>
           <div class="message-card">