For PLUGINS and MODS list support GitHub and Jenkins resolving

- Typically a user probably wants the latest release/build
- Probably could be provided as a custom URL scheme like "github://"
- For both, the last part of the URL would be a file name or glob that uniquely identifies the file within the release/build. If multiple match then it's an error
- Middle part of URL would be org/repo for GitHub or build name for Jenkins
- Not sure where/how to accept the release name/build number and/or allow for indication of "latest"

[Requested in Discord](https://discord.com/channels/660567679458869252/660567682751528981/1257678179167109191)

No implementation files, tests, or entry points are named. Start by locating how PLUGINS and MODS lists currently resolve files, then define the GitHub and Jenkins URL schemes, release/build selection, and multiple-match behavior. Done means both sources resolve the intended unique file and report clear errors for ambiguous matches.

Written by the indexing model from the issue text.