Rock v0

Prove the clip came from the world.

A Rock is the small public proof pack for an attested capture. Verifiers check, in order:

1. Media hash — bytes match media.hash (sha256).
2. Device seal — ed25519 signature over commitment + time.
3. Witnesses — at least one valid sky (or later) witness.
4. Edit proof — published encode traces to sealed capture.
5. Demo flag — demo: true is never production truth.

Location grades: hidden / city / precise. Machine schema: rock-v0.schema.json.