fix: 修复下载按钮显示条件，移除对 canInstall 和 isIOSSafari 的依赖

src/views/pwa/download.vue

@@ -31,7 +31,7 @@ const wasUninstalled = computed(() => {
 
 // 显示下载按钮的条件
 const shouldShowDownloadButton = computed(() => {
-  const result = platform === "browser" && !isInstalled.value && (canInstall.value || isIOSSafari);
+  const result = platform === "browser" && !isInstalled.value;
   console.log("[Download Page] shouldShowDownloadButton:", result);
   return result;
 });