fix: update examples to gpt-5.6-sol - #48

What changed

• update the public README and runnable examples to use gpt-5.6-sol
• keep the bounded live smoke on the new model while preserving the prior none reasoning behavior
• update coupled mocks, assertions, workflow validation, and the protected publish workflow digest

Why

The published README still used gpt-5.4. Existing checks kept README snippets consistent with the runnable examples, but did not keep the selected model current.

Impact

There is no SDK API or type change. The package README and repository examples now show the requested current model, and release smoke verification exercises the same model.

Verification

• npm run test:examples
• npm run test:live-contract
• npm run actionlint
• npm run verify
• independent adversarial diff review