M6.4: Card-grid steps + hybrid origin + clade-restricted backgrounds

Per GODOT_PORTING_GUIDE.md §12, the four "easy" card-grid steps land
together (Species / Calling / Subclass / History), plus three real
features that emerged during testing: cross-step validation gating,
hybrid origin, and clade-restricted background availability.

New step files (Scenes/Steps/):
  StepSpecies.cs    — cards filtered by clade; for hybrids shows two
                      stacked grids (Sire / Dam).
  StepClass.cs      — all classes; class change clears chosen skills
                      and the previously-selected subclass.
  StepSubclass.cs   — subclasses filtered by ClassDef.SubclassIds.
  StepBackground.cs — backgrounds filtered by hybrid + clade rules
                      (see below).

UI/WizardValidation.cs (new):
  Static per-step validators against CharacterDraft. Replaces the
  per-instance Validate() route on the wizard side — Wizard now
  computes the lock state for every step in the flow, not just the
  current one. Mirrors app.jsx's firstIncomplete rule exactly.

  Bug it fixes: previously the wizard checked only the current step's
  validity, so picking a clade let you skip directly to Abilities
  without picking species/calling/etc.

UI/CharacterDraft.cs:
  Phase 6.5 hybrid fields — IsHybrid, SireCladeId, SireSpeciesId,
  DamCladeId, DamSpeciesId, DominantParent. EffectiveCladeId /
  EffectiveSpeciesId resolve to the dominant parent's lineage when
  hybrid; downstream steps don't need to care which path. Helpers
  HasClade(id) and HasAnyCladeOfKind(kind) feed the background
  availability rules.

StepClade.cs:
  Hybrid toggle splits the picker into Sire + Dam grids with a
  Dominant Lineage radio. Validation refuses same-clade Sire+Dam.
  Switched to build-once + mutate-in-place: cards are created once
  during Build(), Refresh just updates Modulate per selection state.
  Tearing down + rebuilding inside the click callback caused
  duplicates because Free() defers when the freed node is mid-signal.

StepBackground.cs:
  Availability rules table — predicates per restricted background id.
  Hybrid-only: passer, hybrid_underground, former_chattel.
  Clade-restricted: warren_runner (Leporidae), pack_raised (Canidae),
  herd_city_born (any prey clade).
  Hybrids match if either parent satisfies the rule.

Other steps (Species/Class/Subclass/Background):
  Refresh dispatched via Callable.From(Refresh).CallDeferred() so the
  rebuild runs after the click handler completes — same Free()-during-
  signal bug as StepClade hit, fixed via deferral instead of mutate-
  in-place because the card lists are dynamic (clade- / class- /
  hybrid-flag-dependent).

Wizard.cs:
  - RebuildStepperStates uses WizardValidation.FirstIncomplete to lock
    every step past the first unsatisfied one.
  - OnStepperClicked checks every step in [0..target-1].
  - UpdateChrome's banner uses WizardValidation for the active step.
  - Scroll preservation moved here (snapshot before step.Refresh
    fires, restore in _Process); StepStats's local copy removed.

Wizard.tscn:
  Scroll node marked unique_name_in_owner so Wizard can grab it.
  PopoverLayer's TraitChip is reused throughout the new step cards.

Aside.cs:
  Hybrid-aware summary — shows "Sire (dominant)" / "Dam" lineage rows
  when IsHybrid; otherwise the existing Clade / Species rows.

Verified end-to-end:
  - Walk Clade → Species → Calling → Subclass → History → Abilities
  - Stepper locks every step past first unsatisfied
  - Hybrid toggle works both directions, dominant changes lineage
  - Hybrid-only and clade-restricted backgrounds appear / disappear
    based on lineage
  - Scroll position preserved across selections
  - Drag-drop still works on Abilities

Closes M6.4. Per guide §12, next is M6.5 — StepSkills (class-driven
choice list with TraitChip per skill).

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

Theriapolis.Godot/Scenes/Steps/StepStats.cs

@@ -37,9 +37,6 @@ public partial class StepStats : VBoxContainer, IStep
     private Button _rollBtn = null!;
     private Button _rerollBtn = null!;
     private Button _autoBtn = null!;
-    private ScrollContainer? _scroll;
-    private int _savedScroll = -1;
-    private bool _scrollPending;
 
     public void Bind(CharacterDraft draft)
     {
@@ -61,7 +58,7 @@ public partial class StepStats : VBoxContainer, IStep
         var intro = new VBoxContainer();
         intro.AddThemeConstantOverride("separation", 6);
         AddChild(intro);
-        intro.AddChild(new Label { Text = "FOLIO V · ABILITIES" });
+        intro.AddChild(new Label { Text = "FOLIO VI · ABILITIES" });
         intro.AddChild(new Label { Text = "Assign your Ability Scores" });
         intro.AddChild(new Label
         {
@@ -139,15 +136,8 @@ public partial class StepStats : VBoxContainer, IStep
     private void Refresh()
     {
         if (_pool is null) return;
-
-        // Tearing down + rebuilding child token trees triggers a layout
-        // pass that resets the parent ScrollContainer's vertical scroll.
-        // Snapshot the scroll position and restore it after the new layout
-        // settles. The restore goes through a method (not SetDeferred on
-        // the property) so it runs reliably after layout finishes — the
-        // method is queued via CallDeferred at the end of Refresh.
-        _scroll = FindAncestorScroll();
-        _savedScroll = _scroll?.ScrollVertical ?? -1;
+        // Scroll preservation now handled centrally by Wizard.UpdateChrome
+        // / Wizard._Process, which snapshots before this Refresh fires.
 
         // Toolbar reflects current method and assignment state.
         bool isRoll = _draft.StatMethod == "roll";
@@ -197,31 +187,6 @@ public partial class StepStats : VBoxContainer, IStep
             }
         }
 
-        // Restore scroll on the next _Process frame — after layout has fully
-        // converged. CallDeferred / SetDeferred / CreateTimer all proved
-        // racy because the ScrollContainer re-clamps scroll on later layout
-        // passes triggered by tree mutations elsewhere.
-        if (_savedScroll >= 0 && _scroll is not null) _scrollPending = true;
-    }
-
-    public override void _Process(double delta)
-    {
-        if (_scrollPending && _scroll is not null && IsInstanceValid(_scroll))
-        {
-            _scroll.ScrollVertical = _savedScroll;
-        }
-        _scrollPending = false;
-    }
-
-    private ScrollContainer? FindAncestorScroll()
-    {
-        Node? n = GetParent();
-        while (n is not null)
-        {
-            if (n is ScrollContainer sc) return sc;
-            n = n.GetParent();
-        }
-        return null;
     }
 
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