Add Engine to Agent infrastructure

[StarshipSuperjam]

Summary

Adds Engine to the Agent infrastructure section.

Why it fits

• Runs terminal-natively through Claude Code and Codex using /engine-* and $engine-* commands.
• The host coding agent reads and writes repositories, runs commands and tests, and prepares pull requests; Engine carries project state, memory, controls, and evidence across sessions.
• Can advance an already-planned build unattended while keeping merge authority with the operator.
• Public, active, and currently has 0 GitHub stars.
• Source-available under Apache-2.0 with the Commons Clause.

The entry is placed after the 1-star entries, following the section's descending star order.

Validation

• Only README.md changes.
• git diff --check passes.
• The repository link, current star count, placement, and license wording were verified before submission.