[codex] Clean up README and Codex router docs

[0xmts]

Summary

• reorder the root README skill list to surface alchemy-cli, alchemy-api, agentic-gateway, then alchemy-codex
• move the alchemy-codex chooser row to the bottom of the skill-selection table and make CLI install the primary installation path
• remove internal Codex plugin packaging and maintenance guidance from the public README, while keeping the small amount of router-specific guidance in the alchemy-codex skill files
• add the official npm link for the Alchemy CLI to the end of the Official Links section

Why

The root README had accumulated internal Codex plugin context that is not useful for external readers. This keeps the public documentation focused on which skill to use and how to install it, while moving the remaining Codex-router context closer to the router skill itself.

Impact

Repo visitors now see the CLI-first workflow first, the skill matrix is easier to scan, and the README no longer carries internal plugin-maintenance instructions.

Validation

• reviewed the diff against origin/main
• ran git diff --cached --check
• verified the commit is signed with the configured SSH signing key