Plan package consumes unified config (init scaffolds, serve/build read paths)
Wire @refrakt-md/plan to the unified refrakt.config.json. plan init scaffolds the config (creating it or extending an existing one with a plan section), and plan serve / plan build / other plan commands read plan.dir from the loaded config instead of relying solely on the --dir flag and defaults. The plan section currently exposes only dir; specs path remains derived from dir (a child folder), and surfacing it as a config field can come later if real-world projects demand it.