feat: 花名册增加职务筛选 + 去掉解聘页新建按钮

- 后端：roster list 接口增加 position 筛选参数
- 后端：新增 /roster/positions 接口返回在职员工职务去重列表
- 前端：花名册筛选栏增加"全部职务"下拉框
- 前端：导出也支持 position 参数
- 前端：去掉解聘补偿页面的"新建解聘"按钮，解聘统一从花名册发起
- 前端：空状态提示改为"请在花名册中选择员工发起解聘"

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

backend/src/routes/roster.routes.ts

@@ -46,6 +46,21 @@ router.get('/departments', authMiddleware, async (req: AuthRequest, res, next) =
   }
 })
 
+/** 花名册可选职务列表（从在职员工中提取去重） */
+router.get('/positions', authMiddleware, async (req: AuthRequest, res, next) => {
+  try {
+    const employees = await prisma.employee.findMany({
+      where: { orgId: req.user!.orgId, status: 'ACTIVE' },
+      select: { position: true },
+      distinct: 'position',
+    })
+    const positions = employees.map((e) => e.position).filter(Boolean).sort()
+    res.json({ success: true, data: positions })
+  } catch (err) {
+    next(err)
+  }
+})
+
 // 花名册列表（含汇总信息，支持分页和过滤）
 router.get('/', authMiddleware, async (req: AuthRequest, res, next) => {
   try {
@@ -55,6 +70,7 @@ router.get('/', authMiddleware, async (req: AuthRequest, res, next) => {
     const status = req.query.status as string  // ACTIVE | PRE_HIRE | RESIGNED
     const contractStatus = req.query.contractStatus as string  // active | expiring | expired | unsigned | etc.
     const department = req.query.department as string
+    const position = req.query.position as string
     const skip = (page - 1) * pageSize
 
     // 使用本地日期午夜，避免时区问题导致当天入职被误判为预入职
@@ -71,6 +87,9 @@ router.get('/', authMiddleware, async (req: AuthRequest, res, next) => {
     if (department) {
       whereBase.department = department
     }
+    if (position) {
+      whereBase.position = position
+    }
     if (search && !isIdCardSearch) {
       whereBase.OR = [
         { name: { contains: search } },