docs(adr): align ADR-039 merge provenance with property stored provenance

[ohdearquant]

Body:

• Problem: ADR-039 merge provenance separator requirements do not match property-stored provenance behavior.
• Proposed fix: amend ADR-039 to bless property-stored provenance, or change append content formatting to meet the ADR separator contract.
• Acceptance criteria: merge provenance has one documented storage format; tests cover the chosen format; docs explain how provenance is recovered after merge.
• Affected crates/ADRs: docs/adr/ADR-039-note-merge.md:1, /Users/lion/khive-work/shows/khive-improvement-survey/roadmap/e2/inventory_adr_feature_migration.md:27.

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Source: khive-improvement-survey show — proposed backlog (propose-only synthesis). Dedup: NEW.