feat(docs): 添加密码学基础文档和mermaid支持

新增密码学基础文档，包含古典加密算法和现代密码学介绍
添加mermaid图表支持以展示密码学概念
在导航栏新增技术理论分类
更新package.json添加mermaid依赖

docs/.vuepress/notes.ts

@@ -57,7 +57,7 @@ const english = defineNoteConfig({
         { text: "阅读提升", link: "/subject/english/reading-writing/" }
       ]
     },
-     {
+    {
       text: "写译", prefix: "/writing-translation", items: [
         { text: "写作与翻译指南", link: "/subject/english/writing-translation/" }
       ]
@@ -97,6 +97,18 @@ const solidity = defineNoteConfig({
     }
   ]
 })
+const cryptography = defineNoteConfig({
+  dir: 'theory',
+  link: '/theory/cryptography/',
+  sidebar: [
+    { text: "密码学基础", link: "/theory/cryptography/" },
+    {
+      text: "古典加密算法", prefix: "/theory", items: [
+        { text: "替换密码", link: "/theory/cryptography/substitution-ciphers/" }
+      ]
+    },
+  ]
+})
 const blockchain = defineNoteConfig({
   dir: 'ops',
   link: '/ops/blockchain',
@@ -135,5 +147,5 @@ const linux = defineNoteConfig({
 export default defineNotesConfig({
   dir: 'notes',
   link: '/',
-  notes: [LeetCode, english, cPlusPlus, solidity, blockchain, linux],
+  notes: [LeetCode, english, cPlusPlus, solidity, blockchain, linux, cryptography],
 })