docs: correct historical Zenodo DOI classification

[papasop]

Correct the repository metadata classification of the earlier Zenodo record.

• identify 10.5281/zenodo.21728432 as a historical version DOI
• retain 10.5281/zenodo.21882158 as the preferred v1.2.9 version DOI
• avoid asserting an unverified all-versions Concept DOI
• preserve the paper-local-ode-v1.5 release boundary
• update repository checksums

Validation:

• SHA256SUMS.txt: PASS, 0 FAILED
• published-paper boundary checker: PASS
• GLOBAL_FLOW_CLAIMED=false
• theorem-bearing paths diff: empty
• manuscript artifact diff: empty
• working tree: clean

Scientific boundary:

• no manuscript changes
• no theorem-bearing asset changes
• no certificate, protocol, JSON, or atlas changes
• no Arb rerun
• no global-flow claim

Excluded actions:

• no tag creation, movement, deletion, or push
• no GitHub Release changes
• no Zenodo changes