refactor(color): unify color sanitizing and picking behind shared components

- Add AKSRT\Core\Color::sanitize($value, $allow_alpha) as the single PHP
  color sanitizer; replace sanitize_hex_color calls and per-class regexes
  (FloatButtons, FieldSchema, ThemeSearch, icon cards, TicketStatusService)
- SchemaProvider / ControllerBase sanitize `color` fields as colors;
  alpha kept only when the schema sets showAlpha
- Split SchemaProvider OAuth validation and option matching into sibling
  traits to stay under the 1000-line limit
- Add AksColorPicker.vue + utils/color.js mirroring the PHP rules; AksField,
  FloatBtnCommonFields and TicketStatusPanel use it
- Widget background color input now uses wpColorPicker
- Remove dead AksCompositeField dimensions/spacing/background branches and
  the unused Gutenberg ColorPicker var
- Add color-unification contract test; update harness requires and tests

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

assets/admin/src/pages/users/partials/ticket/TicketStatusPanel.vue

@@ -72,11 +72,9 @@
                 @click="form.color = swatch"
               />
               <!-- 自定义色：未选中时显示色环，选中后显示当前色并带选中环。 -->
-              <n-color-picker
-                :value="previewColor"
-                :modes="['hex']"
-                :show-alpha="false"
-                @update:value="setColor"
+              <AksColorPicker
+                :model-value="previewColor"
+                @update:model-value="setColor"
               >
                 <template #trigger="{ onClick, ref: setTriggerRef }">
                   <button
@@ -92,7 +90,7 @@
                     @click="onClick"
                   />
                 </template>
-              </n-color-picker>
+              </AksColorPicker>
             </div>
             <n-input
               v-model:value="form.color"
@@ -128,6 +126,8 @@
 import { computed, h, onMounted, ref } from 'vue'
 import { NButton, NSpace, useDialog, useMessage } from 'naive-ui'
 import api from '@/api'
+import AksColorPicker from '@/components/form/AksColorPicker.vue'
+import { toHex } from '@/utils/color.js'
 
 const message = useMessage()
 const dialog = useDialog()
@@ -146,7 +146,6 @@ const editing = ref(null)
 const rows = ref([])
 
 const DEFAULT_COLOR = '#6b7280'
-const HEX_RE = /^#(?:[0-9a-f]{3}|[0-9a-f]{6})$/i
 
 /** 与 TicketStatusService::KEY_PATTERN 保持一致。 */
 const KEY_RE = /^[a-z][a-z0-9_]{1,23}$/
@@ -157,16 +156,6 @@ function normalizeKey(value) {
   return String(value || '').trim().toLowerCase()
 }
 
-/**
- * 归一化为 TicketStatusService::sanitize_color() 接受的小写 #rgb / #rrggbb；
- * 允许省略 #。非法值返回空串。
- */
-function toHex(value) {
-  let hex = String(value || '').trim().toLowerCase()
-  if (hex && !hex.startsWith('#')) hex = `#${hex}`
-  return HEX_RE.test(hex) ? hex : ''
-}
-
 const rules = {
   name: [
     { required: true, message: '请填写状态名称', trigger: 'blur' },
@@ -205,10 +194,7 @@ const currentHex = computed(() => toHex(form.value.color))
 const previewColor = computed(() => currentHex.value || DEFAULT_COLOR)
 const isCustomColor = computed(() => currentHex.value !== '' && !SWATCHES.includes(currentHex.value))
 
-/**
- * 取色器已关闭 alpha（默认开启时回传 #rrggbbaa，会被后端回落成灰色），
- * 这里仍只接受合法十六进制，其余忽略。
- */
+/** AksColorPicker 已归一化为 hex；清空（空串）时保留当前色。 */
 function setColor(value) {
   const hex = toHex(value)
   if (hex) form.value.color = hex