refactor: 移除隐藏的皮肤站会话 iframe

会话改为 API 驱动后，这个隐藏 iframe 只负责收发 postMessage。它每
10 秒检查一次"90 秒内没收到消息就重置会话"，而现在永远收不到消息，
90 秒后必然把刚登录的会话清掉。

删除组件，改由 App.vue 在状态初始化完成后调用 initSkinSiteSession()
恢复登录态。

apps/app-frontend/src/components/ui/SkinSiteSessionFrame.vue

@@ -1,65 +0,0 @@
-<script setup lang="ts">
-import { onMounted, onUnmounted, ref, watch } from 'vue'
-
-import {
-	receiveSkinSiteMessage,
-	resetSkinSiteSession,
-	setSkinSiteFrame,
-	SKIN_SITE_ORIGIN,
-	skinSiteStatus,
-	skinSiteUser,
-} from '@/composables/skin-site-session'
-import { clearHostedSession } from '@/helpers/hosted-packs'
-
-const frame = ref<HTMLIFrameElement>()
-let lastMessage = 0
-let expiryTimer: ReturnType<typeof setInterval> | undefined
-
-watch(
-	[skinSiteStatus, () => skinSiteUser.value?.uuid],
-	() => {
-		void clearHostedSession().catch(() => {})
-	},
-	{ flush: 'sync' },
-)
-
-function connect() {
-	resetSkinSiteSession()
-	lastMessage = 0
-	const contentWindow = frame.value?.contentWindow ?? null
-	setSkinSiteFrame(contentWindow)
-	contentWindow?.postMessage({ type: 'starlight-skin-session-connect' }, SKIN_SITE_ORIGIN)
-}
-
-function receive(event: MessageEvent) {
-	if (receiveSkinSiteMessage(event, frame.value?.contentWindow ?? null)) lastMessage = Date.now()
-}
-
-onMounted(() => {
-	window.addEventListener('message', receive)
-	connect()
-	expiryTimer = setInterval(() => {
-		if (lastMessage && Date.now() - lastMessage > 90_000) resetSkinSiteSession()
-	}, 10_000)
-})
-
-onUnmounted(() => {
-	window.removeEventListener('message', receive)
-	clearInterval(expiryTimer)
-	setSkinSiteFrame(null)
-	resetSkinSiteSession()
-	void clearHostedSession().catch(() => {})
-})
-</script>
-
-<template>
-	<iframe
-		ref="frame"
-		:src="`${SKIN_SITE_ORIGIN}/`"
-		title="StarLight Skin Site session"
-		aria-hidden="true"
-		tabindex="-1"
-		class="pointer-events-none fixed -left-[10000px] top-0 h-px w-px opacity-0"
-		@load="connect"
-	/>
-</template>