Retire the knowledge example once knowledge-system is gone #272

spec/v1/examples/knowledge/ models knowledge-system as it ran before the knowledge platform replaced it (JorisJonkers-dev/fleet-infra#237). Once JorisJonkers-dev/fleet-infra#231 retires knowledge-system, the example describes a project that no longer runs.

When that lands: delete or reduce knowledge/ to what still runs (LightRAG, if it moves), drop knowledge from the worked Platform document's legacy list, and move anything knowledge/rendered/README.md still records as evidence into RENDER-GAPS.md. The knowledge platform example from #201 becomes the worked example for that part of the estate.