fix: 图片预览错误返回可读 503 + feat: PWA 支持(manifest/sw/图标)

public/sw.js

@@ -0,0 +1,33 @@
+const CACHE_NAME = 'bt-preview-v1'
+const SHELL = ['/', '/gate', '/settings', '/manifest.json', '/icon.svg']
+
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => cache.addAll(SHELL)).then(() => self.skipWaiting())
+  )
+})
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(self.clients.claim())
+})
+
+self.addEventListener('fetch', (event) => {
+  const { request } = event
+  const url = new URL(request.url)
+
+  // API、图片预览、下载等动态请求走网络，不做缓存
+  if (url.pathname.startsWith('/api/')) return
+
+  event.respondWith(
+    caches.match(request).then((cached) => {
+      if (cached) return cached
+      return fetch(request).then((res) => {
+        if (request.method === 'GET' && res.status === 200 && res.type === 'basic') {
+          const clone = res.clone()
+          caches.open(CACHE_NAME).then((cache) => cache.put(request, clone)).catch(() => {})
+        }
+        return res
+      })
+    })
+  )
+})