#28 created: fractional seconds so lexicographic==chronological holds

SOURCE: swarm friction #5 (verified: created = second precision "2026-09-08T03:26:43Z"; schema promises lexicographic==chronological order; same-second creates tie on (created,id) -> uuid-random rank -> unstable numbers when import-mirroring a source forge). FIX: new entities' created = RFC3339 with fractional seconds ("...43.123456Z"); parser accepts with AND without fraction (old files parse unchanged); schema [global rules] documents the format. DONE: rapid sequential creates rank in creation order; old files still parse; spec updated.