Issue #3611002: Add a reset option to render-only message stacking

The inverse of sticky: a reset message clears the sticky trail kept before it, so a terminal message (cancellation, rejection) shows on its own. The two flags move under a self-documenting stacking group (stacking.keep + stacking.reset). RenderOnlyInteractionInterface gains resetsEarlier(); InteractionController drops the sticky trail at a reset. Docs + fr.po + the payment example migrated. Verified by ChainTest and MessageInteractionTest.