feat: 完成优化-4全部任务 + 多城市社保 + pgvector修复

- AIAssistant: 会话历史保存/加载/删除，风险预测支持范围筛选，审查结果保存到员工档案
- Dashboard: 待办批量操作，风险分布可下钻，刷新按钮Tab级联，薪税tab导出Excel
- SocialInsurance: 多城市社保/公积金配置支持，城市选择器
- Roster: 新增参保城市字段
- risk.service: 修复风险项去重逻辑(用employeeId:type:actionUrl替代含动态天数的title)
- payroll.routes: 修复OvertimeRecord/Payslip字段名错误
- pgvector: 从源码编译安装x86_64版本兼容postgresql@15
- 优化-4文档: 全部8项标记为已完成

backend/prisma/schema.prisma

@@ -131,6 +131,8 @@ model Organization {
   salaryChangeRecords SalaryChangeRecord[]
   onboardingLinks  OnboardingLink[]
   confirmLinks     ContractConfirmLink[]
+  aiConversations  AIConversation[]
+  aiReviewRecords  AIReviewRecord[]
   socialInsuranceConfig SocialInsuranceConfig[]
   housingFundConfigs   HousingFundConfig[]
   socialInsRecords     EmployeeSocialInsRecord[]
@@ -191,6 +193,7 @@ model Employee {
   housingFundStartMonth String?   // 当前公积金开始年月（便捷字段）
   housingFundEndMonth   String?   // 当前公积金截止年月（便捷字段）
   specialDeduction  Float          @default(0)  // 专项附加扣除（子女教育、赡养老人等，员工portal端填报）
+  city              String?        // 员工社保参保城市
   createdBy         String
   createdAt         DateTime       @default(now())
   updatedAt         DateTime       @updatedAt
@@ -210,6 +213,7 @@ model Employee {
   socialInsRecords    EmployeeSocialInsRecord[]
   housingFundRecords  EmployeeHousingFundRecord[]
   departmentRecords   EmployeeDepartmentRecord[]
+  aiReviewRecords     AIReviewRecord[]
 
   @@unique([orgId, idCardHash])
 }
@@ -342,7 +346,7 @@ model SocialInsuranceConfig {
   createdAt       DateTime @default(now())
   updatedAt       DateTime @updatedAt
 
-  @@unique([orgId, effectiveFrom])
+  @@unique([orgId, city, effectiveFrom])
   @@index([orgId, isCurrent])
 }
 
@@ -363,7 +367,7 @@ model HousingFundConfig {
   createdAt       DateTime @default(now())
   updatedAt       DateTime @updatedAt
 
-  @@unique([orgId, effectiveFrom])
+  @@unique([orgId, city, effectiveFrom])
   @@index([orgId, isCurrent])
 }
 
@@ -666,6 +670,7 @@ model EmployeeSocialInsRecord {
   org          Organization @relation(fields: [orgId], references: [id], onDelete: Cascade)
   employeeId   String
   employee     Employee   @relation(fields: [employeeId], references: [id], onDelete: Cascade)
+  city         String    @default("北京")  // 参保城市
   startMonth   String   // 开始缴费年月 YYYY-MM
   endMonth     String?  // 截止缴费年月 YYYY-MM（null=至今有效）
   base         Float    // 缴费基数
@@ -677,6 +682,7 @@ model EmployeeSocialInsRecord {
 
   @@index([orgId, employeeId])
   @@index([employeeId, startMonth, endMonth])
+  @@index([orgId, city])
 }
 
 model EmployeeHousingFundRecord {
@@ -685,6 +691,7 @@ model EmployeeHousingFundRecord {
   org          Organization @relation(fields: [orgId], references: [id], onDelete: Cascade)
   employeeId   String
   employee     Employee   @relation(fields: [employeeId], references: [id], onDelete: Cascade)
+  city         String    @default("北京")  // 参保城市
   startMonth   String   // 开始缴费年月 YYYY-MM
   endMonth     String?  // 截止缴费年月 YYYY-MM（null=至今有效）
   base         Float    // 缴费基数
@@ -752,3 +759,33 @@ model ContractConfirmLink {
 
   @@index([orgId, status])
 }
+
+// ========== AI 会话 & 审查记录 ==========
+
+model AIConversation {
+  id        String   @id @default(cuid())
+  orgId     String
+  org       Organization @relation(fields: [orgId], references: [id], onDelete: Cascade)
+  userId    String
+  title     String   @default("新对话")
+  messages  Json     // [{ role, content }]
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+
+  @@index([orgId, userId])
+}
+
+model AIReviewRecord {
+  id          String   @id @default(cuid())
+  orgId       String
+  org         Organization @relation(fields: [orgId], references: [id], onDelete: Cascade)
+  employeeId  String?
+  employee    Employee? @relation(fields: [employeeId], references: [id], onDelete: SetNull)
+  type        String   // REVIEW=合同审查, CASE=案例匹配
+  input       String   // 用户输入的合同文本或争议情形
+  result      String   // AI 返回的审查/分析结果
+  createdBy   String
+  createdAt   DateTime @default(now())
+
+  @@index([orgId, employeeId])
+}