onlyworlds 0.7.0

• Folder format v0.3.9, the provenance lines (§4.2). export_world writes two keys into world.json: source, {server, world, at} (the client's API origin, the world's id, and when the export began, as an ISO timestamp in UTC), and exported_as, {kind, role, character}, which slice the key reads. exported_as comes from GET /me through one function, onlyworlds.export.exported_as: an owner key gives {"kind": "owner", "role": "owner", "character": null}, a co-builder or contributor {"kind": "member", "role": <its role>, "character": null}, a guest of any kind (person, agent seat, player) {"kind": "character", "role": "guest", "character": {"id", "name"}} with the name read from GET /character/{id}. When /me is refused or missing, a guest has no Character, or its Character cannot be read, the key is left out: absent, never guessed. FORMAT_VERSION is now "0.3.9"; folders stamped "0.3.8" stay valid.
• Client.me(): GET /me, who this key is ({world, scope, kind, role, membership, character, name?}).
• write_folder keeps source and exported_as like any other world key, so a folder rewritten from a read one (a what-if branch) keeps its parent's verbatim.
• The OKF export carries source and exported_as into world.md's frontmatter as the folder holds them, beside format_version, writable and the snapshot_* keys, so a bundle made from one Character's slice still says so. Before, they would have been noted as not World fields and left out.