Temporal metadata fields (validFrom, validUntil, isCurrent, isRevisionOf)
on UKO InformationUnit nodes enable revision chain tracking: when code
changes, old nodes are marked historical and new revision nodes are
created with back-links. Three storage tiers (hot/warm/cold) filter
nodes by temporal scope (current/recent/all) with configurable retention
(warm_retention_hours default 24h, cold_retention_days default 90d).
Includes TemporalMetadata, TemporalNode, RevisionChain, TierQueryResult,
TierRetentionConfig frozen domain models, TemporalBackend protocol,
InMemoryTemporalBackend stub, TemporalService with structlog and DI,
BackendSet.temporal typing upgrade from object|None to TemporalBackend|None.
67 Behave scenarios, 8 Robot Framework tests, ASV benchmarks, and
reference documentation.
ISSUES CLOSED: #577
