Issue #3611036: Auto mode: the target version materializes lazily, so the Migrate action is missing right after an edit

Enforces the invariant that a workflow version is cut only when an instance pins to it (an instance start or a migration), never as a side effect of viewing a page.

• WorkflowVersionManager: cut-free currentVersionId() and isInstanceCurrent() for display and gating, and migrationTarget() that materializes only at a migration action.
• Versions page no longer materializes on view: it marks "Current" by hash and, when the live shape is edited but uncut, shows a notice and a "Migrate to the current shape" action that cuts the version only on that click.
• Instance list "Migrate to current" gate and the version marker use the cut-free check; the target is resolved (and materialized) at the migrate action.
• Docs and French translations updated; kernel tests cover no-cut-on-read and cut-on-pin.