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/pkb/services/knowledgeBaseService.ts

@@ -7,6 +7,7 @@ import {
   searchKnowledgeBase as ragSearchKnowledgeBase,
   type RagSearchResult,
 } from './ragService.js';
+import { activityService } from '../../../common/services/activity.service.js';
 
 /**
  * 知识库服务
@@ -58,6 +59,26 @@ export async function createKnowledgeBase(
     ekbKbId: result.ekbKbId,
   });
 
+  // 埋点：记录知识库创建
+  try {
+    const userInfo = await prisma.user.findUnique({
+      where: { id: userId },
+      include: { tenants: true }
+    });
+    if (userInfo) {
+      activityService.log(
+        userInfo.tenant_id,
+        userInfo.tenants?.name || null,
+        userId,
+        userInfo.name,
+        'PKB',
+        '创建知识库',
+        'CREATE',
+        name
+      );
+    }
+  } catch (e) { /* 埋点失败不影响主业务 */ }
+
   // 4. 转换BigInt为Number
   return {
     ...knowledgeBase,

backend/src/modules/pkb/services/ragService.ts

@@ -14,6 +14,7 @@ import {
   type SearchResult,
   type IngestResult,
 } from '../../../common/rag/index.js';
+import { activityService } from '../../../common/services/activity.service.js';
 
 // ==================== 类型定义 ====================
 
@@ -65,7 +66,29 @@ export async function searchKnowledgeBase(
   // 查找对应的 EKB 知识库
   const ekbKb = await findOrCreateEkbKnowledgeBase(userId, knowledgeBase.name, knowledgeBase.description);
   
-  return searchWithPgvector(ekbKb.id, query, { topK, minScore, mode });
+  const results = await searchWithPgvector(ekbKb.id, query, { topK, minScore, mode });
+
+  // 埋点：记录 RAG 检索
+  try {
+    const user = await prisma.user.findUnique({
+      where: { id: userId },
+      include: { tenants: true }
+    });
+    if (user) {
+      activityService.log(
+        user.tenant_id,
+        user.tenants?.name || null,
+        userId,
+        user.name,
+        'PKB',
+        'RAG检索',
+        'USE',
+        `kb:${knowledgeBase.name}, results:${results.length}`
+      );
+    }
+  } catch (e) { /* 埋点失败不影响主业务 */ }
+
+  return results;
 }
 
 /**