Display plugin authoring

Display plugin authoring

Plugins receive an immutable PluginContext, expose a stable name, and implement idempotent start() and stop(). PluginRegistry starts them in order, stops them in reverse, rejects duplicate names and override aliases, and isolates lifecycle failures.

Temporary displays claim ScreenArbiter, acquire the context display lock, and recheck ownership before drawing. PeriodicRotatingScreen provides this for fixed sequences. View duration starts only after the claim wins the screen.