refactor: 提取 ModelMultiSelect 组件并支持失效模型检测

- 新增 ModelMultiSelect 组件，支持显示和移除已失效的模型
- 新增 useInvalidModels composable 检测 allowed_models 中的无效引用
- 重构 StandaloneKeyFormDialog 和 UserFormDialog 使用新组件
- 补充 GlobalModel 删除逻辑的设计说明注释

frontend/src/components/common/ModelMultiSelect.vue

@@ -0,0 +1,117 @@
+<template>
+  <div class="space-y-2">
+    <Label class="text-sm font-medium">允许的模型</Label>
+    <div class="relative">
+      <button
+        type="button"
+        class="w-full h-10 px-3 border rounded-lg bg-background text-left flex items-center justify-between hover:bg-muted/50 transition-colors"
+        @click="isOpen = !isOpen"
+      >
+        <span :class="modelValue.length ? 'text-foreground' : 'text-muted-foreground'">
+          {{ modelValue.length ? `已选择 ${modelValue.length} 个` : '全部可用' }}
+          <span
+            v-if="invalidModels.length"
+            class="text-destructive"
+          >({{ invalidModels.length }} 个已失效)</span>
+        </span>
+        <ChevronDown
+          class="h-4 w-4 text-muted-foreground transition-transform"
+          :class="isOpen ? 'rotate-180' : ''"
+        />
+      </button>
+      <div
+        v-if="isOpen"
+        class="fixed inset-0 z-[80]"
+        @click.stop="isOpen = false"
+      />
+      <div
+        v-if="isOpen"
+        class="absolute z-[90] w-full mt-1 bg-popover border rounded-lg shadow-lg max-h-48 overflow-y-auto"
+      >
+        <!-- 失效模型（置顶显示，只能取消选择） -->
+        <div
+          v-for="modelName in invalidModels"
+          :key="modelName"
+          class="flex items-center gap-2 px-3 py-2 hover:bg-muted/50 cursor-pointer bg-destructive/5"
+          @click="removeModel(modelName)"
+        >
+          <input
+            type="checkbox"
+            :checked="true"
+            class="h-4 w-4 rounded border-gray-300 cursor-pointer"
+            @click.stop
+            @change="removeModel(modelName)"
+          >
+          <span class="text-sm text-destructive">{{ modelName }}</span>
+          <span class="text-xs text-destructive/70">(已失效)</span>
+        </div>
+        <!-- 有效模型 -->
+        <div
+          v-for="model in models"
+          :key="model.name"
+          class="flex items-center gap-2 px-3 py-2 hover:bg-muted/50 cursor-pointer"
+          @click="toggleModel(model.name)"
+        >
+          <input
+            type="checkbox"
+            :checked="modelValue.includes(model.name)"
+            class="h-4 w-4 rounded border-gray-300 cursor-pointer"
+            @click.stop
+            @change="toggleModel(model.name)"
+          >
+          <span class="text-sm">{{ model.name }}</span>
+        </div>
+        <div
+          v-if="models.length === 0 && invalidModels.length === 0"
+          class="px-3 py-2 text-sm text-muted-foreground"
+        >
+          暂无可用模型
+        </div>
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref, computed } from 'vue'
+import { Label } from '@/components/ui'
+import { ChevronDown } from 'lucide-vue-next'
+import { useInvalidModels } from '@/composables/useInvalidModels'
+
+export interface ModelWithName {
+  name: string
+}
+
+const props = defineProps<{
+  modelValue: string[]
+  models: ModelWithName[]
+}>()
+
+const emit = defineEmits<{
+  'update:modelValue': [value: string[]]
+}>()
+
+const isOpen = ref(false)
+
+// 检测失效模型
+const { invalidModels } = useInvalidModels(
+  computed(() => props.modelValue),
+  computed(() => props.models)
+)
+
+function toggleModel(name: string) {
+  const newValue = [...props.modelValue]
+  const index = newValue.indexOf(name)
+  if (index === -1) {
+    newValue.push(name)
+  } else {
+    newValue.splice(index, 1)
+  }
+  emit('update:modelValue', newValue)
+}
+
+function removeModel(name: string) {
+  const newValue = props.modelValue.filter(m => m !== name)
+  emit('update:modelValue', newValue)
+}
+</script>

frontend/src/components/common/index.ts

@@ -7,3 +7,6 @@
 export { default as EmptyState } from './EmptyState.vue'
 export { default as AlertDialog } from './AlertDialog.vue'
 export { default as LoadingState } from './LoadingState.vue'
+
+// 表单组件
+export { default as ModelMultiSelect } from './ModelMultiSelect.vue'