Preserve historical ownership after absorbed stack rebuild

[Yehonal]

Summary

• Preserve historical ownership when a published stack is rebuilt from a newer base before an absorbed close.
• Accept the previous source generation only when the stack identity and managed ref are unchanged, the closing generation has exact delivery proof, and the previous tip merges into the current delivery tree without conflict or product changes.
• Add a regression through an immutable old-generation → rebuilt-generation → absorbed-close state chain, plus version 0.45.5 metadata.

Validation

• 42 coordination tests covering historical, absorbed, and reconciliation paths passed locally.
• 3 documentation version tests passed.
• syncwheel validate passed with existing undeclared integration-history warning.
• Python compile, website version check, and diff whitespace check passed.