Checkin now carries disk_free_bytes/disk_total_bytes. Stored on the node doc
(not overwritten by older nodes that don't send them). Node page shows a Disk
row; node cards warn amber under 15% free, red under 5% or 2 GB. A full disk
stopped node-002 recording for 17 days while it showed Online.
Frontend unverified locally (no Node, #207); CI build typechecks.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
