M6.6: StepReview signing + hybrid math revision

- New Step VIII (Review): name input and Confirm button that
  saves the finalized character to user://character.tres.
- Hybrid lineage rules simplified per project decision: drop
  the "no-stack on overlap, take +1 free elsewhere" rule from
  theriapolis-rpg-clades.md. Hybrids now pick one ability mod
  from each parent clade and they sum if they overlap.
  Removes HybridFreeAbility, the free-bonus picker row, and the
  overlap special case from AbilityCalc + WizardValidation.
- StepClade bonus rows now mutate in place (sync ButtonPressed)
  instead of tearing down on every Refresh — the old path freed
  the very button mid-Pressed-signal, leaving stale buttons next
  to the new ones.
- StepSkills drops the redundant "Calling: X · History: Y" meta
  line; both are already shown in the Aside summary.
- Aside hybrid section adds dual-species traits and the
  universal-hybrid detriment pills.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Theriapolis.Godot/UI/WizardValidation.cs

@@ -39,6 +39,15 @@ public static class WizardValidation
             if (string.IsNullOrEmpty(draft.DamCladeId))  return "Pick a dam clade.";
             if (draft.SireCladeId == draft.DamCladeId)
                 return "Sire and dam must be different clades.";
+
+            // Pick one ability mod from each parent clade. Stacking on
+            // the same ability is allowed (the rule was simplified to
+            // permit duplicate picks summing).
+            if (string.IsNullOrEmpty(draft.SireChosenAbility))
+                return "Pick a lineage bonus from the sire clade.";
+            if (string.IsNullOrEmpty(draft.DamChosenAbility))
+                return "Pick a lineage bonus from the dam clade.";
+
             return null;
         }
         return string.IsNullOrEmpty(draft.CladeId) ? "Pick a clade." : null;