feat: 新增启动器界面缩放设置

在高缩放/小屏下，内嵌网页（如皮肤站）顶栏会被裁掉。新增“界面
与外观”中的“启动器缩放”设置，可整体缩放启动器界面。

- 新增 helpers/ui-scale.ts：用 localStorage 保存缩放值（纯本地
  显示偏好，无需后端），并通过 CSS zoom 应用缩放（含内嵌网页）。
- App.vue 启动时调用 installUiScale() 应用已保存的缩放。
- AppearanceSettings.vue 新增缩放设置项：100/110/125/150 预设
  加 50–200 滑条自定义。

apps/app-frontend/src/App.vue

@@ -141,6 +141,7 @@ import {
 	isNetworkMetered,
 	setRestartAfterPendingUpdate,
 } from '@/helpers/utils.js'
+import { installUiScale } from '@/helpers/ui-scale'
 import { start_join_server, start_join_singleplayer_world } from '@/helpers/worlds.ts'
 import i18n, { resolveInitialLocale } from '@/i18n.config'
 import {
@@ -1273,6 +1274,8 @@ provide('previewMinecraftCrashModal', () => minecraftCrashModal.value?.showPrevi
 provide('showLauncherPopup', (_request: unknown) => {})
 provide('showStartupAnnouncement', () => startupAnnouncementModal.value?.show())
 
+installUiScale()
+
 const stateFailed = ref(false)
 stateInitialization
 	.then(() => {

apps/app-frontend/src/components/ui/settings/AppearanceSettings.vue

@@ -26,6 +26,7 @@ import { computed, ref, watch } from 'vue'
 
 import { get, set } from '@/helpers/settings.ts'
 import { getOS } from '@/helpers/utils'
+import { setUiScale, uiScale } from '@/helpers/ui-scale'
 import { useTheming } from '@/store/state'
 import {
 	type AccentColor,
@@ -209,6 +210,23 @@ const messages = defineMessages({
 		defaultMessage:
 			'Enables advanced rendering such as blur effects that may cause performance issues without hardware-accelerated rendering.',
 	},
+	uiScaleTitle: {
+		id: 'app.appearance-settings.ui-scale.title',
+		defaultMessage: 'Launcher scale',
+	},
+	uiScaleDescription: {
+		id: 'app.appearance-settings.ui-scale.description',
+		defaultMessage:
+			'Scale the whole launcher interface. A smaller scale fits more content, which helps when embedded pages are cut off.',
+	},
+	uiScaleCustom: {
+		id: 'app.appearance-settings.ui-scale.custom',
+		defaultMessage: 'Custom',
+	},
+	uiScalePercent: {
+		id: 'app.appearance-settings.ui-scale.percent',
+		defaultMessage: '{value}%',
+	},
 	pageTransitionsTitle: {
 		id: 'app.appearance-settings.page-transitions.title',
 		defaultMessage: 'Page transition animations',
@@ -1020,6 +1038,43 @@ watch(
 					/>
 				</template>
 			</SettingsRow>
+			<SettingsRow stacked>
+				<template #label>
+					<span id="settings-target-appearance-ui-scale" tabindex="-1">
+						{{ formatMessage(messages.uiScaleTitle) }}
+					</span>
+				</template>
+				<template #description>{{ formatMessage(messages.uiScaleDescription) }}</template>
+				<template #control>
+					<div class="flex w-full flex-col gap-3">
+						<div class="flex flex-wrap gap-2">
+							<button
+								v-for="preset in [100, 110, 125, 150]"
+								:key="preset"
+								type="button"
+								class="min-w-16 rounded-lg border border-solid px-3 py-1.5 text-sm font-semibold transition-colors"
+								:class="
+									uiScale === preset
+										? 'border-brand bg-brand-highlight text-brand'
+										: 'border-surface-4 bg-surface-3 text-secondary hover:border-surface-5 hover:text-contrast'
+								"
+								@click="setUiScale(preset)"
+							>
+								{{ preset }}%
+							</button>
+						</div>
+						<Slider
+							id="ui-scale"
+							:model-value="uiScale"
+							:min="50"
+							:max="200"
+							:step="5"
+							unit="%"
+							@update:model-value="(value) => setUiScale(Number(value))"
+						/>
+					</div>
+				</template>
+			</SettingsRow>
 			<SettingsRow>
 				<template #label>
 					<span id="settings-target-appearance-page-transitions" tabindex="-1">

apps/app-frontend/src/helpers/ui-scale.ts

@@ -0,0 +1,60 @@
+import { ref, watch } from 'vue'
+
+/**
+ * 启动器界面缩放（百分比）。
+ * 这是纯本地的显示偏好，用 localStorage 保存即可，无需写入后端设置数据库。
+ */
+const UI_SCALE_STORAGE_KEY = 'starlight-ui-scale'
+const MIN_UI_SCALE = 50
+const MAX_UI_SCALE = 200
+const DEFAULT_UI_SCALE = 100
+
+/** 把缩放值限制在允许范围内。 */
+function clampUiScale(value: number): number {
+	if (!Number.isFinite(value)) return DEFAULT_UI_SCALE
+	return Math.min(MAX_UI_SCALE, Math.max(MIN_UI_SCALE, Math.round(value)))
+}
+
+/** 从 localStorage 读取已保存的缩放值。 */
+function readStoredUiScale(): number {
+	try {
+		const raw = localStorage.getItem(UI_SCALE_STORAGE_KEY)
+		if (raw === null) return DEFAULT_UI_SCALE
+		return clampUiScale(Number(raw))
+	} catch {
+		return DEFAULT_UI_SCALE
+	}
+}
+
+export const uiScale = ref(readStoredUiScale())
+
+export function setUiScale(value: number): void {
+	uiScale.value = clampUiScale(value)
+}
+
+export function resetUiScale(): void {
+	setUiScale(DEFAULT_UI_SCALE)
+}
+
+export { DEFAULT_UI_SCALE, MAX_UI_SCALE, MIN_UI_SCALE }
+
+/** 把缩放应用到文档根节点，并在变化时持久化。 */
+export function installUiScale(): void {
+	const apply = (value: number) => {
+		const factor = String(value / 100)
+		const root = document.documentElement
+		root.style.setProperty('--ui-scale', factor)
+		// 用 CSS zoom 整体缩放界面（含内嵌网页），在 WebView2/WebKit 上最可靠。
+		root.style.setProperty('zoom', factor)
+	}
+
+	apply(uiScale.value)
+	watch(uiScale, (value) => {
+		apply(value)
+		try {
+			localStorage.setItem(UI_SCALE_STORAGE_KEY, String(value))
+		} catch (error) {
+			console.warn('保存界面缩放失败', error)
+		}
+	})
+}