refactor: 第三方库替换 & 代码精简 — v5.1.5

- Markdown 解析器：内联正则 → marked 库（完整 GFM 支持）
- HTML 净化器：内联 DOM 遍历 → DOMPurify（业界标准）
- crypto.ts：删除 sha256js/xorBytes 死代码回退路径
- 消除 5 个文件中 escapeHtml/formatSize 重复定义
- 版本号升级至 5.1.5

package.json

@@ -1,6 +1,6 @@
 {
   "name": "metona-ollama-desktop",
-  "version": "5.1.4",
+  "version": "5.1.5",
   "description": "Metona Ollama - TypeScript + Electron 桌面 AI 聊天客户端",
   "main": "dist/main/main.js",
   "author": "thzxx",
@@ -27,7 +27,9 @@
       "dist/**/*",
       "assets/**/*",
       "!node_modules/**/*",
-      "node_modules/sql.js/**/*"
+      "node_modules/sql.js/**/*",
+      "node_modules/marked/**/*",
+      "node_modules/dompurify/**/*"
     ],
     "extraResources": [
       {
@@ -59,6 +61,7 @@
     }
   },
   "devDependencies": {
+    "@types/dompurify": "^3.0.5",
     "@types/node": "^20.17.0",
     "electron": "^33.4.11",
     "electron-builder": "^25.1.8",
@@ -66,6 +69,8 @@
     "vite": "^5.4.0"
   },
   "dependencies": {
+    "dompurify": "^3.4.0",
+    "marked": "^18.0.2",
     "sql.js": "^1.11.0"
   }
 }