refactor(admin): unify sortable/draggable/repeater list UI

- Add shared sortable-list.css, SORTABLE_LIST_ATTRS and AksSortHandle
- Migrate schema sortable, selected order, inline/modal repeater, sorter,
  floating buttons, footer tabbar and ticket prereply lists to the shared design
- Split AksField.vue (1885 -> 969 lines) into focused components/helpers
- Remove dead AksArrayTable/AksRepeaterField and move-up/down helpers
- Replace hardcoded colors and --n-* vars with --aksrt-color-* tokens

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/admin/src/main.js

@@ -4,6 +4,7 @@ import NaiveUI from 'naive-ui'
 import App from './App.vue'
 import router from './router'
 import './style.css'
+import './styles/sortable-list.css'
 import { styleMountTarget } from './style-target'
 
 const app = createApp(App)