feat(ui): add StringListInput component

Reusable multi-row text input with Add/Remove buttons. Used in the
upcoming refactor of Custom Domains and self-signed Domains / IP
Addresses editors so all three share a single editor pattern.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/src/components/StringListInput/StringListInput.vue

@@ -0,0 +1,57 @@
+<script setup lang="ts">
+defineProps<{
+  placeholder?: string
+  addButtonText?: string
+}>()
+
+const items = defineModel<string[]>({ required: true })
+
+function addItem() {
+  items.value = [...items.value, '']
+}
+
+function removeItem(index: number) {
+  if (items.value.length <= 1)
+    return
+  const next = [...items.value]
+  next.splice(index, 1)
+  items.value = next
+}
+
+function updateItem(index: number, value: string) {
+  const next = [...items.value]
+  next[index] = value
+  items.value = next
+}
+</script>
+
+<template>
+  <div class="space-y-2">
+    <div
+      v-for="(item, index) in items"
+      :key="index"
+      class="flex items-center gap-2"
+    >
+      <AInput
+        :value="item"
+        :placeholder="placeholder"
+        class="flex-1"
+        @update:value="(value: string) => updateItem(index, value)"
+      />
+      <AButton
+        v-if="items.length > 1"
+        type="link"
+        danger
+        @click="removeItem(index)"
+      >
+        {{ $gettext('Remove') }}
+      </AButton>
+    </div>
+    <AButton
+      block
+      @click="addItem"
+    >
+      {{ addButtonText ?? $gettext('Add Item') }}
+    </AButton>
+  </div>
+</template>

app/src/components/StringListInput/index.ts

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+import StringListInput from './StringListInput.vue'
+
+export default StringListInput