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/components/form/AksImageSelectField.vue

@@ -0,0 +1,100 @@
+<template>
+  <div class="aksrt-image-select" role="radiogroup">
+    <button
+      v-for="opt in options"
+      :key="opt.value"
+      type="button"
+      role="radio"
+      class="aksrt-image-select__item"
+      :class="{ 'is-active': modelValue === opt.value }"
+      :aria-checked="modelValue === opt.value"
+      :disabled="disabled"
+      @click="emit('update:modelValue', opt.value)"
+    >
+      <img v-if="opt.image" :src="opt.image" :alt="opt.label" class="aksrt-image-select__img" />
+      <span v-else class="aksrt-image-select__placeholder">
+        <FaIcon :icon="opt.icon || 'fa fas fa-image'" :size="20" />
+      </span>
+      <span class="aksrt-image-select__label">{{ opt.label }}</span>
+    </button>
+  </div>
+</template>
+
+<script setup>
+/** image_select：带预览图的单选。 */
+import FaIcon from './FaIcon.vue'
+
+defineProps({
+  modelValue: { default: null },
+  options: { type: Array, default: () => [] },
+  disabled: { type: Boolean, default: false },
+})
+const emit = defineEmits(['update:modelValue'])
+</script>
+
+<style scoped>
+.aksrt-image-select {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 12px;
+}
+
+.aksrt-image-select__item {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 6px;
+  min-width: 80px;
+  padding: 8px;
+  border: 2px solid var(--aksrt-color-border);
+  border-radius: 8px;
+  background: var(--aksrt-color-surface);
+  cursor: pointer;
+  transition: border-color .15s ease, background-color .15s ease;
+}
+
+.aksrt-image-select__item:hover,
+.aksrt-image-select__item:focus-visible {
+  outline: none;
+  border-color: var(--aksrt-color-primary);
+}
+
+.aksrt-image-select__item.is-active {
+  border-color: var(--aksrt-color-primary);
+  background: var(--aksrt-color-primary-soft);
+}
+
+.aksrt-image-select__item:disabled {
+  cursor: not-allowed;
+}
+
+.aksrt-image-select__img {
+  width: 60px;
+  height: 60px;
+  object-fit: cover;
+  border-radius: 4px;
+}
+
+.aksrt-image-select__placeholder {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 60px;
+  height: 60px;
+  border-radius: 4px;
+  background: var(--aksrt-color-canvas);
+  color: var(--aksrt-color-border-strong);
+}
+
+.aksrt-image-select__label {
+  color: var(--aksrt-color-text-secondary);
+  font-size: 11px;
+  text-align: center;
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .aksrt-image-select__item {
+    transition: none;
+  }
+}
+</style>