Document WorkOS device login after installation

[las7]

What changed

• Make reachpad auth login the primary onboarding path in the public README.
• Explain the --no-browser flow for remote machines.
• Keep the manual credential handoff as a recovery path.
• Print the browser login command after installation.
• Prune private-monorepo-only packages from the public lockfile after Cargo resolved the standalone four-crate workspace.

Verification

Greentree passed the complete standalone workspace test command for tree 1b80c21c6689195e63b352285a29064cc1b81b64.