Export bundles that boot elsewhere

scribase export is here, and the promise is now executable.

• Produces a bundle with schema, table data, auth users, storage bytes, and policies — not just a database dump.
• Ships a checksummed manifest (sha256 over ordered artifact digests) so you can verify the bundle before trusting it.
• The boots_elsewhere acceptance test is green: an exported bundle starts up as a runnable stack.
• Available in the CLI, the /v1 API (POST /v1/…/projects/{id}/export), and the console.