fix(landing): serve hosted install.sh wrapper

[YOMXXX]

Fixes #4136

Why

I hit this while checking the hosted install path from the issue. https://open-design.ai/install.sh was falling through to the landing-page HTML app, so curl | sh received markup instead of shell and failed immediately.

The actual MCP installer logic already lives in od mcp install. This PR adds a thin hosted shell wrapper so the URL returns executable shell while keeping the product-owned installer in the CLI.

What users will see

curl -fsSL https://open-design.ai/install.sh | sh -s <agent> now receives a shell script that delegates to od mcp install <agent> [options]. The wrapper prints help for --help, fails clearly if od is missing, and rejects non-Open-Design od binaries such as Linux/WSL coreutils /usr/bin/od.

The README also documents the hosted equivalent next to the existing od mcp install <agent> command.

Surface area

• UI — new page / dialog / panel / menu item / setting / empty state in apps/web or apps/desktop (including Electron menu bar)
• Keyboard shortcut — new or changed
• CLI / env var — new od subcommand or flag, new tools-dev / tools-pack / tools-pr flag, or new OD_* env var
• API / contract — new /api/* endpoint, new SSE event, or changed shape in packages/contracts
• Extension point — new entry under skills/, design-systems/, design-templates/, or craft/, or change to the skills protocol
• i18n keys — added new translation keys (see TRANSLATIONS.md for the locale workflow)
• New top-level dependency — adding any new entry to the root package.json (dependencies or devDependencies); workspace-package package.json files are out of scope. Include a paragraph on what we get vs. what bytes we ship (see CONTRIBUTING.md → Code style)
• Default behavior change — changes what existing users experience without opting in (default model, default setting, file/SQLite schema, auto-network on startup, auto-install)
• None — internal refactor, docs, tests, or translation update only

Screenshots

No screenshot attached. This is a static hosted shell asset and README update, not a visual UI change.

Bug fix verification

• Test path that reproduces the bug: apps/landing-page/tests/install-sh-static.test.ts
• Did the test go red on main and green on this branch? yes — the red case was the missing apps/landing-page/public/install.sh static asset, which meant the hosted route fell back to the HTML app.

Validation

• PATH=/Users/liguanchen/.nvm/versions/node/v24.15.0/bin:$PATH pnpm --filter @open-design/landing-page test — 29 tests passed
• PATH=/Users/liguanchen/.nvm/versions/node/v24.15.0/bin:$PATH pnpm --filter @open-design/landing-page build
• PATH=/Users/liguanchen/.nvm/versions/node/v24.15.0/bin:$PATH pnpm guard
• PATH=/Users/liguanchen/.nvm/versions/node/v24.15.0/bin:$PATH pnpm typecheck

[lefarcen]

🧪 This PR changes a user-facing install path, so it needs a manual QA pass before merge — please hold off self-merging for now. We'll loop QA in once it's merge-ready.

[nettee]

I found one blocking issue in the new install.sh shadowed-od validation path; details are inline.

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[lefarcen]

Hey @YOMXXX — the current blocker is the one @nettee called out on this head: the shadowed-od guard still accepts binaries that return success for od mcp install --help, so the wrapper can fall through to the wrong executable instead of surfacing the shadowing error.

Once that check validates an Open-Design-specific marker in the help output and the regression test covers the success-exit / non-Open-Design case, this should be ready for another look.

💡 To drive this PR to merge hands-free, paste this to your AI coding agent (Claude Code / Codex / opencode / Cursor …):
Take over nexu-io/open-design#4866 until it merges — read https://raw.githubusercontent.com/nexu-io/looper/main/skills/pr-takeover/SKILL.md and follow it.

[nettee]

I found one non-blocking maintainability issue in the new install.sh identity probe; details are inline.

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[nettee]

@YOMXXX I re-reviewed the updated hosted installer path on 592aed3f, including the CLI-owned probe token, the landing-page wrapper, and the regression coverage for shadowed od handling. The current shape closes the earlier shadowing and help-text drift concerns cleanly, and the wrapper now fails fast before delegating to a non-Open-Design binary. I wasn’t able to rerun the package tests in this checkout because node_modules are absent here, but the changed-range logic and test coverage line up with the fix. Thanks for iterating on this quickly and tightening the contract between the hosted script and the CLI.

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[lefarcen]

Thanks for the quick turnaround, @YOMXXX — the current head is clear from the earlier review blocker, and I'm queueing the manual QA pass next.

[lefarcen]

Thanks @kokisanai — quick status check from our side: this PR isn't waiting on maintainer review right now. @nettee already approved the current head, and the remaining step is the manual QA pass that's already queued.

@YOMXXX If QA finds anything we'll keep the thread moving here, but there isn't a review blocker from the team at the moment.

[AmyShang-alt]

QA 验收记录

验收范围：

• 验证 hosted install.sh 不再落到 landing-page HTML fallback。
• 验证 wrapper 能通过稳定 CLI probe 识别 Open Design od，正常委托 od mcp install <agent> [options]。
• 验证 Linux/WSL 常见的非 Open Design od shadowing 会 fail fast，不会继续执行错误二进制。
• 验证 landing-page build 与 daemon CLI probe 类型/测试边界。

已验证：

• PR head: 592aed3f437d7dc79c3856098c37a5e30368c748。
• pnpm install --frozen-lockfile 通过。
• pnpm --filter @open-design/landing-page test -- install-sh-static 通过：30 tests passed。
• pnpm --filter @open-design/daemon exec vitest run -c vitest.config.ts tests/mcp-install-cli.test.ts 通过：1 test passed。
• pnpm --filter @open-design/landing-page build 通过，只有既有 warning/hints，无 error。
• pnpm --filter @open-design/daemon typecheck 通过。
• 手工抽验 install.sh --help、缺少 <agent>、fake Open Design od 正常委托、fake/coreutils 风格 od 拒绝均符合预期。
• 本地 landing preview 访问 /install.sh 返回 shell 脚本内容，不是 HTML fallback。

未验证：

• 未验证线上 https://open-design.ai/install.sh 部署后的实际响应；该项需等 PR 合并/部署后做最终 curl 抽验。

风险/关注点：

• 这是公开安装入口，用户影响较高；当前回归测试和手工抽验已覆盖主要失败模式。

结论：

• 验收通过。当前 head 可移除 needs-validation 并标记 validated。