Good first issues - switching from URL to FilePath.

[jglogan]

One area we could use some help with in the coming month is replacing URL with SystemPackage.FilePath. If you're interested in getting started with contributions to container, this is a great way to start familiarizing yourself with the code.

#1480 is one such PR. While Claude and friends can chew through the entire project and convert everything, we'd prefer that if you're going to take this on, to file an issue for the smallest reviewable change, such as for a single type/API or cluster of tightly coupled types/APIs. This makes it far simpler for us to review and approve the changes.