release: codewith 0.1.91

[andrei-hasna]

Summary

• bump the Codewith Cargo workspace release version from 0.1.90 to 0.1.91
• regenerate only workspace package versions in Cargo.lock
• add focused 0.1.91 release notes for the workflow activation retry fix merged in PR fix(workflows): bound activation database contention #572

Validation

• just fmt
• cargo metadata --locked --format-version 1 --no-deps
• Codewith release-version contract tests
• changelog version/tag/npm/compare binding checks
• Cargo.lock scope check: 129 version-only 0.1.90 to 0.1.91 pairs
• staged secrets scan: 3 files, 0 findings
• exact commit patch secrets scan: 0 findings
• npm @hasna/codewith@0.1.91 absence: E404
• remote rust-v0.1.91 tag absence: confirmed

Task: COD2-00010 (9facf31d-38ab-4a22-8a66-f6121615512f)
Predecessor: PR #572, merged at 4b75a92c690b454fe8a7e2a4435c2bb9e50fe058

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