Fix retained artifact health refresh

[waple0820]

What changed

• refresh stored validation per immutable Revision when validator semantics change
• preserve HTML bytes, lineage, publication pointers, and share metadata during health refresh
• upgrade only the exact official v1 Welcome Revision without replacing user catalog metadata
• recompute imported archive history with the current validator

Verification

• 21 Python tests
• JS syntax checks and git diff check
• browser IndexedDB smoke including non-empty lineage, legacy share, and workflow pointers
• independent review: no blocking findings