feat(admin): fuzzy search by email/ID, display full userId in user list

- Backend: add email + _id to  filter in getUsers() for fuzzy search
- Frontend: show full MongoDB _id in user row with tap-to-copy
- Search placeholder updated to mention email/ID

backend/src/modules/admin/admin.controller.ts

@@ -85,7 +85,12 @@ export class AdminController {
       filter.$or = [
         { phone: { $regex: escaped, $options: 'i' } },
         { nickname: { $regex: escaped, $options: 'i' } },
+        { email: { $regex: escaped, $options: 'i' } },
       ]
+      // 支持按 MongoDB _id 搜索（24位 hex）
+      if (/^[0-9a-f]{24}$/i.test(keyword)) {
+        filter.$or.push({ _id: keyword })
+      }
     }
     const skip = (Math.max(1, +page) - 1) * +limit
     const [users, total] = await Promise.all([