feat(docs): add interactive demo components for technical appendices

Add placeholder Vue components for visualizing technical concepts across multiple domains including frontend routing, browser rendering, cache design, queue design, database principles, API design, cloud services, and backend evolution. These components provide interactive educational content for the documentation.

Update documentation structure to include new appendix sections and enhance existing content with visual components. Remove unused 'codex' dependency from package.json.

docs/.vitepress/theme/components/appendix/cache-design/CacheArchitectureOverview.vue

@@ -0,0 +1,50 @@
+<template>
+  <div class="demo-container">
+    <div class="demo-header">
+      <h4>{{ title }}</h4>
+      <p class="hint">{{ description }}</p>
+    </div>
+    <div class="demo-content">
+      <el-alert type="info" :closable="false">
+        缓存架构概览演示组件占位符 - 待实现具体交互
+      </el-alert>
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { ref } from 'vue'
+
+const title = ref('缓存架构概览')
+const description = ref('展示缓存系统的整体架构，包括本地缓存、分布式缓存、CDN缓存等多级缓存架构')
+</script>
+
+<style scoped>
+.demo-container {
+  border: 1px solid var(--vp-c-divider);
+  border-radius: 8px;
+  padding: 20px;
+  background: var(--vp-c-bg-soft);
+}
+
+.demo-header {
+  margin-bottom: 20px;
+}
+
+.demo-header h4 {
+  margin: 0 0 8px 0;
+  color: var(--vp-c-text-1);
+}
+
+.hint {
+  margin: 0;
+  font-size: 14px;
+  color: var(--vp-c-text-2);
+}
+
+.demo-content {
+  display: flex;
+  flex-direction: column;
+  gap: 16px;
+}
+</style>