chore(infra): 配置ESLint 9 flat config并恢复lint-staged集成

- 新增 eslint.config.js（ESLint 9 flat config 格式）
- 安装 @eslint/js + typescript-eslint + eslint-config-prettier
- 6 个 TS 服务 lint 脚本：eslint src --ext .ts → eslint src
- lint-staged 恢复 eslint --fix
- .gitignore 忽略 docker-compose.minimal.override.yml
- known-issues.md 新增 P6 硬化条目

services/content/package.json

@@ -8,7 +8,7 @@
     "build": "nest build",
     "start": "node dist/main.js",
     "test": "vitest run",
-    "lint": "eslint src --ext .ts",
+    "lint": "eslint src",
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {