feat(admin): Add activity logs page and fix AI chat markdown rendering

- Add paginated activity logs API with filters (date, module, action, keyword)

- Add ActivityLogsPage with table, filters, and detail modal

- Add markdown rendering support for AI chat messages

- Remove prototype placeholder content from chat sidebar

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/modules/admin/controllers/statsController.ts

@@ -98,6 +98,81 @@ export async function getUserOverview(
   }
 }
 
+/**
+ * 分页查询运营日志
+ * GET /api/admin/stats/logs
+ * 
+ * 查询参数:
+ * - page: 页码 (默认1)
+ * - pageSize: 每页条数 (默认20, 最大100)
+ * - startDate: 开始日期 (YYYY-MM-DD)
+ * - endDate: 结束日期 (YYYY-MM-DD)
+ * - module: 模块筛选
+ * - action: 动作筛选
+ * - keyword: 关键词搜索 (用户名/租户名)
+ */
+export async function getActivityLogs(
+  request: FastifyRequest<{
+    Querystring: {
+      page?: string;
+      pageSize?: string;
+      startDate?: string;
+      endDate?: string;
+      module?: string;
+      action?: string;
+      keyword?: string;
+    }
+  }>,
+  reply: FastifyReply
+) {
+  try {
+    const {
+      page: pageStr,
+      pageSize: pageSizeStr,
+      startDate: startDateStr,
+      endDate: endDateStr,
+      module,
+      action,
+      keyword,
+    } = request.query;
+
+    // 解析分页参数
+    const page = Math.max(1, Number(pageStr) || 1);
+    const pageSize = Math.min(100, Math.max(1, Number(pageSizeStr) || 20));
+
+    // 解析日期参数
+    const startDate = startDateStr ? new Date(startDateStr) : undefined;
+    const endDate = endDateStr ? new Date(endDateStr) : undefined;
+
+    const result = await activityService.getActivityLogs({
+      page,
+      pageSize,
+      startDate,
+      endDate,
+      module,
+      action,
+      keyword,
+    });
+
+    return reply.send({
+      success: true,
+      data: result.data,
+      pagination: {
+        page: result.page,
+        pageSize: result.pageSize,
+        total: result.total,
+        totalPages: Math.ceil(result.total / result.pageSize),
+      },
+    });
+  } catch (error: any) {
+    logger.error('[StatsController] 获取运营日志失败', { error: error.message });
+    return reply.status(500).send({
+      success: false,
+      message: error.message || '获取运营日志失败',
+    });
+  }
+}
+
 /**
  * 清理过期日志（管理接口）
  * POST /api/admin/stats/cleanup