feat: 发薪日期多选+提前N天提醒+电子签设置区域修复

- Schema: 去掉 payrollFrequency，新增 payrollDays (JSON数组) + payrollReminderDays (Int)
- 设置页: 发薪日期改为1-28号多选按钮，新增提前提醒天数设置
- 设置页: 恢复电子签署设置区域（3个开关：规章制度/工资条/入职文件）
- 工作日历: 发薪日期作为 PAYROLL_DAY 事件显示
- 工作台: 提前N天提醒发薪日期，N可配置
- TaskCenter: 新增发薪提醒分类图标
- seed文件: 更新为 payrollDays 格式

backend/src/routes/dashboard.routes.ts

@@ -285,6 +285,43 @@ router.get('/workspace/next-actions', authMiddleware, async (req: AuthRequest, r
       take: 10,
     })
 
+    // 5. 发薪日提前提醒
+    const org = await prisma.organization.findUnique({
+      where: { id: orgId },
+      select: { payrollDays: true, payrollReminderDays: true },
+    })
+    const payrollDays = Array.isArray(org?.payrollDays) ? org.payrollDays as number[] : []
+    const reminderDays = org?.payrollReminderDays ?? 3
+    const payrollReminderItems: any[] = []
+    const currentYear = now.getFullYear()
+    const currentMonth = now.getMonth() // 0-indexed
+    for (const day of payrollDays) {
+      // 本月发薪日
+      const thisMonthPayday = new Date(currentYear, currentMonth, day)
+      const diffDays = Math.floor((thisMonthPayday.getTime() - now.getTime()) / 86400000)
+      if (diffDays >= 0 && diffDays <= reminderDays) {
+        payrollReminderItems.push({
+          id: `payroll-${currentYear}-${currentMonth + 1}-${day}`,
+          title: `发薪日（每月${day}号）${diffDays === 0 ? '今天' : `${diffDays}天后`}`,
+          subtitle: diffDays === 0 ? '今天发薪' : `还有${diffDays}天`,
+          link: '/money',
+        })
+      }
+      // 下月发薪日（如果当月已过，看下月）
+      if (diffDays < 0) {
+        const nextMonthPayday = new Date(currentYear, currentMonth + 1, day)
+        const nextDiffDays = Math.floor((nextMonthPayday.getTime() - now.getTime()) / 86400000)
+        if (nextDiffDays >= 0 && nextDiffDays <= reminderDays) {
+          payrollReminderItems.push({
+            id: `payroll-${currentYear}-${currentMonth + 2}-${day}`,
+            title: `发薪日（下月${day}号）${nextDiffDays === 0 ? '今天' : `${nextDiffDays}天后`}`,
+            subtitle: `还有${nextDiffDays}天`,
+            link: '/money',
+          })
+        }
+      }
+    }
+
     // 按优先级分组
     const actions: Array<{ category: string; priority: 'high' | 'medium' | 'low'; items: any[] }> = [
       {
@@ -333,6 +370,11 @@ router.get('/workspace/next-actions', authMiddleware, async (req: AuthRequest, r
           link: '/special-status',
         })),
       },
+      {
+        category: '发薪提醒',
+        priority: 'medium',
+        items: payrollReminderItems,
+      },
     ]
 
     // 过滤空分类