docs: add VitePress documentation site

- Add docs directory with VitePress configuration
- Add GitHub Actions workflow for docs build and deploy
- Support bilingual (English/Chinese) documentation
- Include search, custom theme, and responsive design

docs/.vitepress/theme/components/SkipLink.vue

@@ -0,0 +1,42 @@
+<script setup lang="ts">
+/**
+ * Skip Link Component
+ * Accessibility feature allowing keyboard users to skip to main content
+ */
+</script>
+
+<template>
+  <a href="#VPContent" class="skip-link">
+    Skip to main content
+  </a>
+</template>
+
+<style scoped>
+.skip-link {
+  position: absolute;
+  top: -100px;
+  left: 0;
+  padding: 8px 16px;
+  background: var(--vp-c-primary);
+  color: white;
+  text-decoration: none;
+  z-index: 9999;
+  transition: top 0.3s ease;
+  font-size: 14px;
+  font-weight: 500;
+}
+
+.skip-link:focus {
+  top: 0;
+}
+
+.skip-link:hover {
+  background: var(--vp-c-primary-600);
+}
+
+@media print {
+  .skip-link {
+    display: none;
+  }
+}
+</style>