Document when Sigima contract versions change (provenance page, agent instructions) #432

Problem

The provenance page says that a replay needs a contract qualified for the recorded version, but not when a contract version changes. The instructions for AI agents show Sigima computation functions without their operation contract and do not mention the versioning rule.

The rule (DataLab-Platform/Sigima#96): Sigima increases the version of a contract whenever a change of the computation changes its result, whatever the releases of DataLab; activities recorded with an earlier version are then refused explicitly. Keeping version 1 in Sigima 1.4 was a one-off exception.

Proposal

• doc/features/common/provenance.rst (and French translation): explain the rule and its consequence (explicit refusal, compute again to record with the current version), link to the Sigima page "Operation contracts and versions".
• .github/copilot-instructions.md: Sigima examples with operation_id, contract_version and qualification; the versioning rule and the provenance tests to update.