fix: 提升管理端启动与导航稳定性

- 等待初始路由就绪并提供可恢复的启动失败页面

- 收敛失效登录导航并按需加载 SVG 图标资源

easyflow-ui-admin/app/src/startup-error.ts

@@ -0,0 +1,45 @@
+interface RenderStartupErrorOptions {
+  reload?: () => void;
+  root?: HTMLElement | null;
+}
+
+/**
+ * 在 Vue 应用尚未挂载时展示可恢复的启动错误，避免异常后只剩白屏。
+ */
+function renderStartupError(options: RenderStartupErrorOptions = {}) {
+  const root = options.root ?? document.querySelector<HTMLElement>('#app');
+  if (!root) {
+    return false;
+  }
+
+  const container = document.createElement('main');
+  container.className = 'startup-error';
+  container.setAttribute('role', 'alert');
+
+  const content = document.createElement('div');
+  content.className = 'startup-error__content';
+
+  const title = document.createElement('h1');
+  title.className = 'startup-error__title';
+  title.textContent = '页面加载失败';
+
+  const description = document.createElement('p');
+  description.className = 'startup-error__description';
+  description.textContent = '请刷新后重试';
+
+  const retryButton = document.createElement('button');
+  retryButton.className = 'startup-error__retry';
+  retryButton.type = 'button';
+  retryButton.textContent = '重新加载';
+  retryButton.addEventListener('click', () => {
+    (options.reload ?? (() => window.location.reload()))();
+  });
+
+  content.append(title, description, retryButton);
+  container.append(content);
+  root.replaceChildren(container);
+  retryButton.focus();
+  return true;
+}
+
+export { renderStartupError };