backdraft 0.17.0

A week on output an agent can act on without scraping, and on refusing to answer from a registry this build cannot fully see.

• ingest --json prints one backdraft/ingest-v1 object: for each source that landed its slug, outcome (created, generation, unchanged), whether it came back thin or was restored, whether --slug applied, and whether its page images were captured; failures with each reason; and notes, the report's own strings. A failed source still exits 1, with the object on stdout saying what landed. --dry-run --json is the same object before anything is written.
• doctor --json prints one backdraft/doctor-v1 object, each capability with ready, gap, costs and its key as set or absent (never a value), and the registry's entry adds its root, schema version and document count. Plain doctor now names the schema version too.
• The registry carries a schema version, and a build refuses one written by a newer backdraft at exit 1 with nothing changed, naming both versions and the upgrade. export reports the version beside $format. Older releases cannot see the stamp, so the guard protects this version and later ones.
• forget names each draft whose last bind cited the source, and how many citations each would turn unresolved, before it asks, under --yes too, and when it refuses for want of --yes.
• verify reports a registry that will not open through its usual error rather than a traceback.

1797 tests.