fix: resolve 9 P0+P1 review findings (bills decorators, campus isolation bypass, ding raw crash, batch import counter, SSE multi-tab, interval leak, dept permissions, cycle prevention, tree depth)

apps/server/src/students/students.service.ts

@@ -142,6 +142,7 @@ export class StudentsService {
           tenantId: row.tenantId || undefined,
         }),
       );
+      imported++;
     }
     return {
       message: `成功导入 ${imported} 名学生，跳过 ${skipped} 条（重复或空行）`,