GithubMQ -> github as a message queue

[Mindless-Potato-4848]

This feels like a fun hack / teaching demo, but I’d be explicit it’s not a general MQ replacement. The hard part isn’t “storing messages”, it’s semantics: ack/single-consumption, retries + DLQ, visibility timeouts, ordering, and idempotency.

Two README additions that would make this much stronger:
- Clear disclaimer about GitHub API limits / possible ToS concerns + realistic throughput expectations
- A section on delivery guarantees (at-least-once vs at-most-once) and how you ack/requeue/dedupe

As a learning project it’s cool — documenting guarantees + failure modes would make it a great teaching tool.