fix: resolve 3 review findings (permission codes, profile guard, JSDoc)

backend/src/rbac/rbac.service.ts

@@ -20,6 +20,7 @@ const PRESET_PERMISSIONS: Array<{ code: string; name: string; group: string }> =
   { code: 'occupancy:checkin', name: '办理入住', group: 'occupancy' },
   { code: 'occupancy:checkout', name: '办理退宿', group: 'occupancy' },
   { code: 'occupancy:transfer', name: '调换宿舍', group: 'occupancy' },
+  { code: 'occupancy:delete', name: '删除入住记录', group: 'occupancy' },
   { code: 'expense:view', name: '查看费用', group: 'expense' },
   { code: 'expense:create', name: '录入费用', group: 'expense' },
   { code: 'expense:edit', name: '编辑费用', group: 'expense' },