I'm mostly writing code for myself, but it's a project that'll end up being public and it'll be available for others to do whatever they want with. Does that change the answer?

I hate it when a comment tells me to see JIRA-1234. What if in a year's time we stop using Jira?

Far too often the answer has been that it doesn't matter, because the reason you stopped using Jira is the company stopped sending paycheques.

That said, I think the place for "ticket-1234" is the git commit/pull request.

Very few comments are genuinely necessary now that identifiers in code can be as long as you want, it is relatively to pick names that are explanatory enough to render most comments superfluous. 1% exceptions for unusual algorithms. (You're using named consts/enums rather than magic numbers, yes?)