scene.migrate_v6_to_v7

Converts a v6 scene's scene.json to the v7 format, in place and user-initiated only — the migration never runs automatically. v6 scenes carry top-level player{} and camera{} object blocks; v7 replaces both with a single top-level string player intent, either "spawns" or "none", decided from the v6 player.required_in_play flag. On "spawns" it injects the final-shape PlayerSetups/Spawns structure that mirrors the scene.assetType template — a DefaultSocialPlayer prototype with a child body carrying the avatar asset and an owner-scoped camera rig, and a DefaultSpawn pointing back at it — with injected ids derived from the scene folder so no two converted scenes collide. Every existing entity, the lighting, and the format are preserved untouched. It also scans the sibling entrypoint.luau for references to the removed player/camera flow and returns the flagged call sites for review without ever rewriting the Luau. It is idempotent and safe: a scene already at version 7 or higher is skipped, and a scene with a missing, too-new, or invalid version is reported as an error without being mutated. Reach for it to bring an old scene onto the current player system.