bldng1337/dion-runtime ? reverse-engineered prompt

Build me the runtime for a media reader extension system.

I want a small but solid core that can load and run extensions, expose the basic hooks they need, and make it easy for the reader app to talk to them. It should feel reliable, work well with the Rust side of the project, and leave room for the JavaScript and Dart parts that are already in this repo.

Please make the project easy to run and test locally, with clear defaults and a simple developer workflow. If there are missing details in how these extensions are supposed to work, look up current docs online or infer the cleanest approach from the existing codebase and keep it practical. I care more about getting a usable runtime in place than perfect completeness, so build the core path well and keep the rest straightforward to extend later.