Replace the folding rules.

⚠ THIS MOVES REAL HOURS BETWEEN PLAN CATEGORIES, so it is gated and attributed. The caller must be signed in (the router requires it), the rules are validated before anything is written, and each rule records who saved it and when — a change that reshapes every per-category figure should never be anonymous.

⚠ VALIDATED, NOT TRUSTED. A rule folding a label into a category the plan does not contain would silently move hours into a bucket that renders nowhere; two rules for one label would make the result depend on list order. Both are refused here rather than absorbed.