Split AdminDialogs.vue into per-dialog components

Break the monolithic admin dialog component into a thin dispatcher plus
one component per dialog type under admin/dialogs/, with a shared
AdminDialog frame (Modal wrapper, title, error and Cancel/Save actions).
No functional change. Also drop two unused input refs (nameInput,
displayNameInput).

frontend/src/admin/dialogs/AdminDialog.vue

@@ -0,0 +1,51 @@
+<script setup>
+import Modal from '@/components/Modal.vue'
+
+// Shared frame for the admin dialogs: Modal wrapper, title, form with
+// error display and Cancel/Save actions. The dialog's fields go in the
+// default slot; optional extra content attached next to the modal panel
+// (e.g. the domain origins diagnostics) goes in the 'attached' slot.
+defineProps({
+  title: { type: String, required: true },
+  busy: Boolean,
+  error: { type: String, default: '' },
+  submitLabel: { type: String, default: 'Save' },
+  // Block submit (e.g. while domain-origin validation has hard errors)
+  submitDisabled: Boolean,
+  // Name-edit dialogs render their own error message and action buttons
+  // — the frame then only provides the title and the form element
+  bare: Boolean
+})
+
+defineEmits(['submit', 'close'])
+</script>
+
+<template>
+  <Modal @close="$emit('close')">
+    <template #attached>
+      <slot name="attached" />
+    </template>
+    <h3 class="modal-title">{{ title }}</h3>
+    <form @submit.prevent="$emit('submit')" class="modal-form">
+      <slot />
+      <div v-if="error && !bare" class="error small">{{ error }}</div>
+      <div v-if="!bare" class="modal-actions">
+        <button
+          type="button"
+          class="btn-secondary"
+          @click="$emit('close')"
+          :disabled="busy"
+        >
+          Cancel
+        </button>
+        <button
+          type="submit"
+          class="btn-primary"
+          :disabled="busy || submitDisabled"
+        >
+          {{ submitLabel }}
+        </button>
+      </div>
+    </form>
+  </Modal>
+</template>