fix(ios): 修复 iOS 端输入框聚焦导致页面自动缩放

iOS Safari 在输入框字号小于 16px 时聚焦会自动放大页面，且失焦后不会恢复，
导致布局错位。启动时仅对 iOS 设备为 viewport 注入 maximum-scale=1 阻止该
行为；iOS 10+ 用户仍可双指手动缩放，Android 不受影响。

- utils/device.ts 新增 detectIOSDevice/isIOSDevice（含 iPadOS 桌面模式识别）
- main.ts 启动阶段执行 initIOSViewportZoomFix
- 补充 detectIOSDevice 单元测试

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/main.ts

@@ -5,8 +5,23 @@ import router from './router'
 import i18n, { initI18n } from './i18n'
 import { useAppStore } from '@/stores/app'
 import { updateFavicon } from '@/utils/branding'
+import { isIOSDevice } from '@/utils/device'
 import './style.css'
 
+function initIOSViewportZoomFix() {
+  // iOS Safari 在输入框字号小于 16px 时聚焦会自动放大页面，且失焦后不会恢复。
+  // 限制 maximum-scale 可阻止该行为；iOS 10+ 用户仍可双指手动缩放，不影响可访问性。
+  // 仅在 iOS 设备上注入，避免影响 Android Chrome 的手动缩放能力。
+  if (!isIOSDevice()) return
+
+  const viewport = document.querySelector('meta[name="viewport"]')
+  if (!viewport) return
+
+  const content = viewport.getAttribute('content') || ''
+  if (/maximum-scale/i.test(content)) return
+  viewport.setAttribute('content', `${content}, maximum-scale=1.0`)
+}
+
 function initThemeClass() {
   const savedTheme = localStorage.getItem('theme')
   const shouldUseDark =
@@ -18,6 +33,7 @@ function initThemeClass() {
 async function bootstrap() {
   // Apply theme class globally before app mount to keep all routes consistent.
   initThemeClass()
+  initIOSViewportZoomFix()
 
   const app = createApp(App)
   const pinia = createPinia()

frontend/src/utils/__tests__/device.spec.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { detectMobileDevice } from '../device'
+import { detectIOSDevice, detectMobileDevice } from '../device'
 
 describe('detectMobileDevice', () => {
   it('prefers userAgentData.mobile when available', () => {
@@ -53,3 +53,43 @@ describe('detectMobileDevice', () => {
     })).toBe(false)
   })
 })
+
+describe('detectIOSDevice', () => {
+  it('recognizes iPhone from the UA token', () => {
+    expect(detectIOSDevice({
+      navigator: {
+        userAgent: 'Mozilla/5.0 (iPhone; CPU iPhone OS 17_5 like Mac OS X) AppleWebKit/605.1.15 Version/17.5 Mobile/15E148 Safari/604.1',
+        maxTouchPoints: 5,
+      },
+    })).toBe(true)
+  })
+
+  it('recognizes iPadOS desktop mode via touch capability', () => {
+    expect(detectIOSDevice({
+      navigator: {
+        userAgent: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15) AppleWebKit/605.1.15 Version/17.0 Safari/605.1.15',
+        platform: 'MacIntel',
+        maxTouchPoints: 5,
+      },
+    })).toBe(true)
+  })
+
+  it('keeps Android devices as non-iOS', () => {
+    expect(detectIOSDevice({
+      navigator: {
+        userAgent: 'Mozilla/5.0 (Linux; Android 14; Pixel 8) AppleWebKit/537.36 Chrome/136.0 Mobile Safari/537.36',
+        maxTouchPoints: 5,
+      },
+    })).toBe(false)
+  })
+
+  it('keeps desktop macOS without touch as non-iOS', () => {
+    expect(detectIOSDevice({
+      navigator: {
+        userAgent: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 Chrome/136.0 Safari/537.36',
+        platform: 'MacIntel',
+        maxTouchPoints: 0,
+      },
+    })).toBe(false)
+  })
+})

frontend/src/utils/device.ts

@@ -20,6 +20,7 @@ interface DeviceDetectionEnvironment {
 
 const MOBILE_UA_RE = /\b(Mobi|Android|iPhone|iPod|Windows Phone|webOS|BlackBerry|IEMobile)\b/i
 const TABLET_UA_RE = /\b(iPad|Tablet)\b/i
+const IOS_UA_RE = /\b(iPhone|iPad|iPod)\b/i
 
 function matchesQuery(
   matchMedia: DeviceDetectionEnvironment['matchMedia'],
@@ -60,3 +61,21 @@ export function isMobileDevice(): boolean {
     matchMedia: typeof window !== 'undefined' ? window.matchMedia.bind(window) : undefined,
   })
 }
+
+export function detectIOSDevice(env: DeviceDetectionEnvironment = {}): boolean {
+  const nav = env.navigator
+  if (!nav) return false
+
+  const userAgent = nav.userAgent || ''
+  const maxTouchPoints = nav.maxTouchPoints ?? 0
+  // iPadOS 13+ 桌面模式下 UA 伪装成 macOS，需要靠触控点数识别。
+  const isIPadOSDesktopMode = nav.platform === 'MacIntel' && maxTouchPoints > 1
+
+  return IOS_UA_RE.test(userAgent) || isIPadOSDesktopMode
+}
+
+export function isIOSDevice(): boolean {
+  if (typeof navigator === 'undefined') return false
+
+  return detectIOSDevice({ navigator })
+}