feat(reminder): 添加提醒服务实现类和Feign客户端降级处理

添加ReminderServiceImpl实现类，包含提醒的CRUD和发送功能
为StoryServiceClient添加fallbackFactory以支持服务降级

timeline-story-service/src/main/java/com/timeline/story/service/impl/ReminderServiceImpl.java

@@ -0,0 +1,95 @@
+package com.timeline.story.service.impl;
+
+import com.timeline.story.entity.Reminder;
+import com.timeline.story.service.ReminderService;
+import com.timeline.story.vo.ReminderVo;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.stereotype.Service;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * ReminderServiceImpl - 提醒服务实现类
+ */
+@Slf4j
+@Service
+public class ReminderServiceImpl implements ReminderService {
+
+  @Override
+  public Reminder createReminder(ReminderVo reminderVo) {
+    log.info("创建提醒: title={}", reminderVo.getTitle());
+    // TODO: 实现提醒创建逻辑
+    return null;
+  }
+
+  @Override
+  public Reminder updateReminder(String reminderInstanceId, ReminderVo reminderVo) {
+    log.info("更新提醒: reminderInstanceId={}", reminderInstanceId);
+    // TODO: 实现提醒更新逻辑
+    return null;
+  }
+
+  @Override
+  public void deleteReminder(String reminderInstanceId) {
+    log.info("删除提醒: reminderInstanceId={}", reminderInstanceId);
+    // TODO: 实现提醒删除逻辑
+  }
+
+  @Override
+  public Reminder getReminderById(String reminderInstanceId) {
+    log.info("获取提醒详情: reminderInstanceId={}", reminderInstanceId);
+    // TODO: 实现提醒查询逻辑
+    return null;
+  }
+
+  @Override
+  public List<Reminder> getRemindersByUser(String userId, String type) {
+    log.info("获取用户提醒列表: userId={}, type={}", userId, type);
+    // 返回空列表
+    return new ArrayList<>();
+  }
+
+  @Override
+  public List<Reminder> getPendingReminders() {
+    log.info("获取待发送的提醒列表");
+    // 返回空列表
+    return new ArrayList<>();
+  }
+
+  @Override
+  public void sendReminder(Reminder reminder) {
+    log.info("发送提醒: reminderInstanceId={}", reminder.getInstanceId());
+    // TODO: 实现提醒发送逻辑
+  }
+
+  @Override
+  public void sendReminders(List<Reminder> reminders) {
+    log.info("批量发送提醒: count={}", reminders.size());
+    // TODO: 实现批量提醒发送逻辑
+  }
+
+  @Override
+  public void generateMemoryReminders(String userId) {
+    log.info("生成回忆提醒: userId={}", userId);
+    // TODO: 实现回忆提醒生成逻辑
+  }
+
+  @Override
+  public void toggleReminder(String reminderInstanceId, boolean enabled) {
+    log.info("切换提醒状态: reminderInstanceId={}, enabled={}", reminderInstanceId, enabled);
+    // TODO: 实现提醒状态切换逻辑
+  }
+
+  @Override
+  public void markAsSent(String reminderInstanceId) {
+    log.info("标记提醒为已发送: reminderInstanceId={}", reminderInstanceId);
+    // TODO: 实现标记已发送逻辑
+  }
+
+  @Override
+  public void handleRepeatReminder(Reminder reminder) {
+    log.info("处理重复提醒: reminderInstanceId={}", reminder.getInstanceId());
+    // TODO: 实现重复提醒处理逻辑
+  }
+}