Serve install.sh from the web app

[princepal9120]

https://multica.ai/install.sh currently returns a 404, even though the repo already has an installer script in scripts/install.sh.

This PR serves that existing script from the web app at /install.sh, so the published install URL works without adding another copy of the script or depending on a redirect.

What changed:

• Added apps/web/app/install.sh/route.ts.
• The route reads scripts/install.sh from the repo and returns it as text/x-shellscript.
• Added a focused route test that checks the response status, content type, shebang, and usage text.

Closes #1984.

Validation:

git diff --cached --check

I also ran a small Node check to verify the route resolves to scripts/install.sh, and that the script starts with #!/usr/bin/env bash and includes Usage: install.sh.

I attempted the targeted web test as well:

corepack pnpm --filter @multica/web test -- app/install.sh/route.test.ts

That could not run in this checkout because dependencies were not installed, and corepack pnpm install --frozen-lockfile failed with ERR_PNPM_ENOSPC on the runner filesystem.

[vercel]

@princepal9120 is attempting to deploy a commit to the IndexLabs Team on Vercel.

A member of the Team first needs to authorize it.

[forrestchang]

dup #1949