feat: 实例分组增强前端（拖拽分组 UI）

移植 Axolotl 的拖拽式实例分组界面到 Starlight，接入阶段1的规范化分组后端：

- 新增 helpers/analytics.ts（trackEvent 遥测桩）
- 补全 helpers/instance-groups.ts（6 个 invoke 包装）
- 新增 composables/useInstanceGroups.ts（分组状态 + 事件监听）
- 升级 composables/useGridGrouping.ts（排序方向 isSortAscending/toggleSortDirection）
- helpers/events.js 补 instance_groups_listener（对接 instance_groups_changed 事件）
- 新增 components/ui/library/DraggableInstanceCard.vue
- 新增 components/ui/library/InstanceGroup.vue（并补 group-drag-handle 修复组拖拽重排）
- 新增 components/ui/modal/InstanceGroupModal.vue
- GridDisplay.vue 替换为 Axolotl 拖拽版（DragDropProvider + vuedraggable）
- 补 en-US/zh-CN i18n 键各 39 条

apps/app-frontend/src/components/ui/library/DraggableInstanceCard.vue

@@ -0,0 +1,92 @@
+<script setup lang="ts">
+import { KeyboardSensor, PointerSensor, useDraggable } from '@dnd-kit/vue'
+import { useEventListener } from '@vueuse/core'
+import { computed, ref } from 'vue'
+
+import type { GameInstance } from '@/helpers/types'
+
+const props = defineProps<{
+	instance: GameInstance
+	instanceGroupId: string
+	disabled: boolean
+}>()
+
+const emit = defineEmits<{
+	(e: 'contextmenu' | 'card-click', event: MouseEvent): void
+	(e: 'start-long-press' | 'cancel-long-press'): void
+}>()
+
+const cardElement = ref<HTMLElement>()
+
+const instanceCardSensors = [
+	PointerSensor.configure({
+		preventActivation: () => false,
+	}),
+	KeyboardSensor,
+]
+
+const dragDisabled = computed(() => props.disabled)
+
+const { isDragging } = useDraggable({
+	id: computed(() => `instance:${props.instanceGroupId}:${props.instance.id}`),
+	element: cardElement,
+	disabled: dragDisabled,
+	sensors: instanceCardSensors,
+	data: computed(() => ({
+		instanceId: props.instance.id,
+		fromGroup: props.instanceGroupId,
+	})),
+})
+
+let wantsClick = false
+
+useEventListener(window, 'pointerdown', () => {
+	wantsClick = true
+})
+useEventListener(window, 'pointerup', () => {
+	if (isDragging.value) {
+		wantsClick = false
+	}
+})
+useEventListener(window, 'blur', () => {
+	wantsClick = false
+})
+
+function onCardClick(event: MouseEvent) {
+	if (!wantsClick || isDragging.value) return
+	wantsClick = false
+	emit('card-click', event)
+}
+
+function onContextMenu(event: MouseEvent) {
+	emit('contextmenu', event)
+}
+
+function onMouseDown() {
+	if (!dragDisabled.value) {
+		emit('start-long-press')
+	}
+}
+
+function onMouseUp() {
+	emit('cancel-long-press')
+}
+</script>
+
+<template>
+	<div
+		ref="cardElement"
+		class="group relative min-w-0 w-full"
+		@click="onCardClick"
+		@mousedown="onMouseDown"
+		@mouseup="onMouseUp"
+		@mouseleave="onMouseUp"
+		@touchstart="!dragDisabled && onMouseDown()"
+		@touchend="onMouseUp"
+		@touchcancel="onMouseUp"
+		@contextmenu.prevent.stop="onContextMenu"
+	>
+		<slot :is-dragging="isDragging" />
+		<slot v-if="!isDragging" name="overlay" />
+	</div>
+</template>