feat(harness): 用戶 CC harness（acr install-harness）+ 公開 repo 只留對外

讓「用 arcrun 開發」的用戶，他的 CC 自動載入 arcrun 防護、不退回自寫 Python。

新增 user-cc-harness（SDD: .agents/specs/user-cc-harness，本機）：
- acr install-harness：冪等裝進用戶當前專案（新/舊專案皆可），acr init 末尾也順便裝
  - CLAUDE.md arcrun 區塊（標記包夾，append 不破壞既有）
  - .claude/skills/arcrun-mindset（世界觀 + 資源去哪取 acr parts/auth-recipe）
  - .claude/commands/arcrun.md（/arcrun slash command）
  - .claude/hooks/arcrun-guard.sh（python→提醒不硬擋、暴露→exit 2、每條含正路）
  - settings.json 合併 hook（不覆蓋用戶既有 hooks/設定）
- llms.txt + README「給 AI」段：第一接觸點（用戶丟連結，CC 讀了知道第一步 install-harness）
  含 CF 憑證白話照抄式引導（不對用戶講 KV/Worker/R2 術語）
- harness 素材內嵌 npm 套件（cli/harness/，files 帶上），不依賴用戶有 arcrun repo
- 實測：空目錄/冪等/既有檔合併皆通過，tsc exit 0，npm pack 含 harness 5 檔

公開 repo 清理（richblack：用戶要用不要開發 arcrun）：
- git rm --cached 移除開發痕跡 + 思考過程出公開 repo（本機保留供 richblack 開發）：
  .claude/CLAUDE.md/AGENTS.md/.agents/docs/DECISIONS/BACKLOG/landing/.github
- .gitignore 防回流；補 MIT LICENSE

MCP（P7）納入 install-harness/update 的接點已設計，實作待 MCP 對齊（BACKLOG 另一條線）。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

landing/README.md

@@ -1,36 +0,0 @@
-This is a [Next.js](https://nextjs.org) project bootstrapped with [`create-next-app`](https://nextjs.org/docs/app/api-reference/cli/create-next-app).
-
-## Getting Started
-
-First, run the development server:
-
-```bash
-npm run dev
-# or
-yarn dev
-# or
-pnpm dev
-# or
-bun dev
-```
-
-Open [http://localhost:3000](http://localhost:3000) with your browser to see the result.
-
-You can start editing the page by modifying `app/page.tsx`. The page auto-updates as you edit the file.
-
-This project uses [`next/font`](https://nextjs.org/docs/app/building-your-application/optimizing/fonts) to automatically optimize and load [Geist](https://vercel.com/font), a new font family for Vercel.
-
-## Learn More
-
-To learn more about Next.js, take a look at the following resources:
-
-- [Next.js Documentation](https://nextjs.org/docs) - learn about Next.js features and API.
-- [Learn Next.js](https://nextjs.org/learn) - an interactive Next.js tutorial.
-
-You can check out [the Next.js GitHub repository](https://github.com/vercel/next.js) - your feedback and contributions are welcome!
-
-## Deploy on Vercel
-
-The easiest way to deploy your Next.js app is to use the [Vercel Platform](https://vercel.com/new?utm_medium=default-template&filter=next.js&utm_source=create-next-app&utm_campaign=create-next-app-readme) from the creators of Next.js.
-
-Check out our [Next.js deployment documentation](https://nextjs.org/docs/app/building-your-application/deploying) for more details.