Add a hosted Bash installer for devos CLI

[0xroylee]

Summary

• Add a public GET /cli endpoint in the landing app that serves a POSIX shell installer as plain text.
• The installer detects platform and architecture, enforces a minimum Bun version, installs devos globally with Bun, and prints PATH/onboarding guidance.
• Add focused tests for the route and installer behavior, and exclude landing tests from Next typecheck so they do not leak into app type validation.

Testing

• bun test packages/landing/tests/install-script.test.ts
• bun run --filter landing typecheck
• bun run --filter landing build
• bun run check
• bun run typecheck
• bun test