test(10-05): bring every SPA module, composable and component under Vitest

- 41 unit and component suites under admin/tests/{app,state,shell,list,form,relation,views,ui}
  covering states and a11y roles; every src module is imported by a test
- typed fixture helper assigns each JSON fixture to its generated OpenAPI type
- fix: iconFor ignores inherited object members such as "constructor"
- fix: field controls import ./control instead of the registry (import cycle
  left a renderer unregistered depending on module load order)
- fix: dropdown shows the placeholder for an unknown stored value next to an emptyOption
- fix: list announces a failed schema load even when the rows arrive after it
- tailwind no longer scans admin/tests; boardwalk/dist rebuilt

admin/src/components/form/fields/DropdownField.vue

@@ -3,7 +3,7 @@ import { computed } from 'vue'
 import { ChevronDown } from '@lucide/vue'
 import type { FormOption } from '../../../api/types'
 import { t } from '../../../app/i18n'
-import { controlClass, type FieldControlProps } from '../registry'
+import { controlClass, type FieldControlProps } from '../control'
 
 const props = defineProps<FieldControlProps>()
 const emit = defineEmits<{ 'update:modelValue': [value: FormOption['value']] }>()
@@ -63,7 +63,9 @@ function onChange(event: Event): void {
       @change="onChange"
     >
       <option v-if="field.emptyOption !== undefined" :value="EMPTY" class="text-muted">{{ field.emptyOption }}</option>
-      <option v-else-if="selected === PLACEHOLDER" :value="PLACEHOLDER" disabled>
+      <!-- A stored value no option matches shows the placeholder, never a
+           wrong choice (also next to an emptyOption). -->
+      <option v-if="selected === PLACEHOLDER" :value="PLACEHOLDER" disabled>
         {{ t('backend::lang.form.select_placeholder') }}
       </option>
       <option v-for="(option, index) in options" :key="index" :value="String(index)" class="text-text">