Improvements for llms.txt

[earth2marsh]

Now that https://aep.dev/llms.txt is live, starting an issue for tracking improvements:

• Following this issue it may be useful to offer different flavors of AEPs for proto vs OpenAPI, like: /protobuf/llms.txt and /openapi/llms.txt.
• The may/should/must content is handled with html. That's not terrible, but maybe just allcaps would suffice for llms.txt?
• The references like [MAINTAINERS.md](https://github.com/aep-dev/aep.dev/blob/main/MAINTAINERS.md) or [nested collections]: /122.md#collection-identifiers refer to the markdown on GitHub, when it is prob better to refer to the publish HTML pages?
• It might be handy to put a kind of "self" link after each AEP heading, e.g., # AEP-3 Glossary. That should make it more obvious for how to cite the individual rule on the web.