feat(docs): add NavGrid/NavCard components and restructure stage pages

- Add NavGrid.vue and NavCard.vue components for better navigation layout
- Restructure stage-0 index pages across languages into intro.md with new navigation components
- Remove old stage-0 index.md files and update stage-3 pages similarly
- Add new dependencies 'claude' and 'codex' to package.json
- Improve code formatting in multiple Vue components for better readability
- Update documentation content and structure for better user experience

docs/.vitepress/theme/components/NavCard.vue

@@ -0,0 +1,78 @@
+<script setup>
+defineProps({
+  href: {
+    type: String,
+    required: true
+  },
+  title: {
+    type: String,
+    required: true
+  },
+  description: {
+    type: String,
+    default: ''
+  },
+  icon: {
+    type: String,
+    default: ''
+  }
+})
+</script>
+
+<template>
+  <a :href="href" class="nav-card-link">
+    <div class="nav-card">
+      <div class="card-header">
+        <span v-if="icon" class="card-icon">{{ icon }}</span>
+        <span class="card-title">{{ title }}</span>
+      </div>
+      <div v-if="description" class="card-desc">{{ description }}</div>
+    </div>
+  </a>
+</template>
+
+<style scoped>
+.nav-card-link {
+  text-decoration: none !important;
+  color: inherit !important;
+  display: block;
+}
+
+.nav-card {
+  border: 1px solid var(--vp-c-divider);
+  border-radius: 12px;
+  padding: 16px;
+  transition: all 0.3s ease;
+  background: var(--vp-c-bg-soft);
+  height: 100%;
+}
+
+.nav-card:hover {
+  border-color: var(--vp-c-brand);
+  transform: translateY(-2px);
+  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
+}
+
+.card-header {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  margin-bottom: 8px;
+}
+
+.card-icon {
+  font-size: 20px;
+}
+
+.card-title {
+  font-weight: 600;
+  color: var(--vp-c-brand);
+  font-size: 14px;
+}
+
+.card-desc {
+  color: var(--vp-c-text-2);
+  font-size: 14px;
+  line-height: 1.5;
+}
+</style>