feat: 事件关注功能优化 - Redux 乐观更新 + Mock 数据状态同步

1. communityDataSlice 添加事件关注乐观更新
   - pending: 立即切换 isFollowing 状态
   - rejected: 回滚到之前状态
   - fulfilled: 使用 API 返回的准确数据覆盖

2. Mock 数据添加内存状态管理
   - 新增 followedEventsSet 和 followedEventsMap 存储
   - toggleEventFollowStatus: 切换关注状态
   - isEventFollowed: 检查是否已关注
   - getFollowedEvents: 获取关注事件列表

3. Mock handlers 使用内存状态
   - follow handler: 使用 toggleEventFollowStatus
   - following handler: 使用 getFollowedEvents 动态返回
   - 事件详情: 返回正确的 is_following 状态

修复: 关注事件后导航栏"自选事件"列表不同步更新的问题

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/store/slices/communityDataSlice.js

@@ -608,14 +608,40 @@ const communityDataSlice = createSlice({
         state.error[stateKey] = action.payload;
         logger.error('CommunityData', `${stateKey} 加载失败`, new Error(action.payload));
       })
-      // toggleEventFollow
+      // ===== toggleEventFollow（乐观更新）=====
+      // pending: 立即切换状态
+      .addCase(toggleEventFollow.pending, (state, action) => {
+        const eventId = action.meta.arg;
+        const current = state.eventFollowStatus[eventId];
+        // 乐观切换：如果当前已关注则变为未关注，反之亦然
+        state.eventFollowStatus[eventId] = {
+          isFollowing: !(current?.isFollowing),
+          followerCount: current?.followerCount ?? 0
+        };
+        logger.debug('CommunityData', 'toggleEventFollow pending (乐观更新)', {
+          eventId,
+          newIsFollowing: !(current?.isFollowing)
+        });
+      })
+      // rejected: 回滚状态
+      .addCase(toggleEventFollow.rejected, (state, action) => {
+        const eventId = action.meta.arg;
+        const current = state.eventFollowStatus[eventId];
+        // 回滚：恢复到之前的状态（再次切换回去）
+        state.eventFollowStatus[eventId] = {
+          isFollowing: !(current?.isFollowing),
+          followerCount: current?.followerCount ?? 0
+        };
+        logger.error('CommunityData', 'toggleEventFollow rejected (已回滚)', {
+          eventId,
+          error: action.payload
+        });
+      })
+      // fulfilled: 使用 API 返回的准确数据覆盖
       .addCase(toggleEventFollow.fulfilled, (state, action) => {
         const { eventId, isFollowing, followerCount } = action.payload;
         state.eventFollowStatus[eventId] = { isFollowing, followerCount };
         logger.debug('CommunityData', 'toggleEventFollow fulfilled', { eventId, isFollowing, followerCount });
-      })
-      .addCase(toggleEventFollow.rejected, (_state, action) => {
-        logger.error('CommunityData', 'toggleEventFollow rejected', action.payload);
       });
   }
 });