feat(admin): Implement operational monitoring MVP and login optimization

Summary:
- Add SimpleLog table for activity tracking (admin_schema)
- Implement ActivityService with fire-and-forget pattern
- Add stats API endpoints (overview/live-feed/user-overview/cleanup)
- Complete activity logging for 7 modules (SYSTEM/AIA/PKB/ASL/DC/RVW/IIT)
- Update Admin Dashboard with DAU/DAT metrics and live feed
- Fix user module permission display logic
- Fix login redirect to /ai-qa instead of homepage
- Replace top navigation LOGO with brand image
- Fix PKB workspace layout CSS conflict (rename to .pa-chat-container)

New files:
- backend/src/common/services/activity.service.ts
- backend/src/modules/admin/controllers/statsController.ts
- backend/src/modules/admin/routes/statsRoutes.ts
- frontend-v2/src/modules/admin/api/statsApi.ts
- docs/03-.../04-operational-monitoring-mvp-plan.md
- docs/03-.../04-operational-monitoring-mvp-implementation.md

Tested: All features verified locally

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

@@ -0,0 +1,126 @@
+/**
+ * Stats Controller - 运营统计控制器
+ * 
+ * 提供运营看板数据接口
+ * 
+ * @version 1.0.0
+ * @date 2026-01-25
+ */
+
+import type { FastifyRequest, FastifyReply } from 'fastify';
+import { activityService } from '../../../common/services/activity.service.js';
+import { logger } from '../../../common/logging/index.js';
+
+/**
+ * 获取今日大盘数据
+ * GET /api/admin/stats/overview
+ */
+export async function getOverview(
+  request: FastifyRequest,
+  reply: FastifyReply
+) {
+  try {
+    const data = await activityService.getTodayOverview();
+    return reply.send({
+      success: true,
+      data,
+    });
+  } catch (error: any) {
+    logger.error('[StatsController] 获取大盘数据失败', { error: error.message });
+    return reply.status(500).send({
+      success: false,
+      message: error.message || '获取大盘数据失败',
+    });
+  }
+}
+
+/**
+ * 获取实时流水账
+ * GET /api/admin/stats/live-feed?limit=100
+ */
+export async function getLiveFeed(
+  request: FastifyRequest<{ Querystring: { limit?: string } }>,
+  reply: FastifyReply
+) {
+  try {
+    const limit = Math.min(Number(request.query.limit) || 100, 500); // 最大500条
+    const data = await activityService.getLiveFeed(limit);
+    return reply.send({
+      success: true,
+      data,
+    });
+  } catch (error: any) {
+    logger.error('[StatsController] 获取流水账失败', { error: error.message });
+    return reply.status(500).send({
+      success: false,
+      message: error.message || '获取流水账失败',
+    });
+  }
+}
+
+/**
+ * 获取用户360画像
+ * GET /api/admin/users/:id/overview
+ */
+export async function getUserOverview(
+  request: FastifyRequest<{ Params: { id: string } }>,
+  reply: FastifyReply
+) {
+  try {
+    const { id } = request.params;
+    
+    if (!id) {
+      return reply.status(400).send({
+        success: false,
+        message: '用户ID不能为空',
+      });
+    }
+
+    const data = await activityService.getUserOverview(id);
+    
+    if (!data.profile) {
+      return reply.status(404).send({
+        success: false,
+        message: '用户不存在',
+      });
+    }
+
+    return reply.send({
+      success: true,
+      data,
+    });
+  } catch (error: any) {
+    logger.error('[StatsController] 获取用户画像失败', { error: error.message });
+    return reply.status(500).send({
+      success: false,
+      message: error.message || '获取用户画像失败',
+    });
+  }
+}
+
+/**
+ * 清理过期日志（管理接口）
+ * POST /api/admin/stats/cleanup
+ */
+export async function cleanupLogs(
+  request: FastifyRequest,
+  reply: FastifyReply
+) {
+  try {
+    const deletedCount = await activityService.cleanupOldLogs();
+    return reply.send({
+      success: true,
+      data: {
+        deletedCount,
+        message: `已清理 ${deletedCount} 条过期日志`,
+      },
+    });
+  } catch (error: any) {
+    logger.error('[StatsController] 清理日志失败', { error: error.message });
+    return reply.status(500).send({
+      success: false,
+      message: error.message || '清理日志失败',
+    });
+  }
+}
+