feat: 添加 knip 冗余代码检查工具

配置 knip.json 检测未使用的文件、exports、依赖等。
新增 check:unused script，运行 knip-bun 扫描死代码。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -17,7 +17,8 @@
         "lint:fix": "biome check --fix src/",
         "format": "biome format --write src/",
         "prepare": "git config core.hooksPath .githooks",
-        "test": "bun test"
+        "test": "bun test",
+        "check:unused": "knip-bun"
     },
     "dependencies": {
         "@alcalzone/ansi-tokenize": "^0.3.0",
@@ -132,6 +133,7 @@
         "@types/react-reconciler": "^0.33.0",
         "@types/sharp": "^0.32.0",
         "@types/turndown": "^5.0.6",
+        "knip": "^6.1.1",
         "typescript": "^6.0.2"
     }
 }