M6.13: Sex picker + species variant schema

Adds character Sex (male/female) as a top-level CharacterDraft field
required for every character, and species variants as a layer on top
of the base species record. Two variant axes:

  - "sex": auto-resolves from CharacterDraft.Sex for purebreds; for
           hybrids, pinned by parent role (sire = male, dam = female)
           by definition. No picker needed beyond Step 0.
  - "lineage": explicit per-species pick (Ram-Folk's sheep/goat). Has
               its own picker on Step 1 (purebred path under the grid;
               hybrid path embedded into the per-parent pick column).

Schema (Theriapolis.Core/Data):
  - SpeciesDef gains VariantAxis (string) and Variants (array of
    SpeciesVariantDef { Id, Name, Traits, Detriments }).
  - JSON content not yet populated — that's M6.14.

CharacterDraft adds:
  - Sex (required by Step 0 validation)
  - SpeciesVariant / SireSpeciesVariant / DamSpeciesVariant
  - ResolveVariantId(species, role) that returns the active variant
    id for a given context — used by Aside to layer variant traits
    onto the base species traits.

Step 0 (StepClade): sex picker row above the hybrid toggle. Two
toggle buttons radio-style.

Step 1 (StepSpecies): purebred path renders a lineage picker below
the grid when the picked species has VariantAxis == "lineage";
hybrid path embeds a lineage picker at the top of each parent's
pick column. Hover popovers summarise each variant's contents.

Validation: Sex is required at Step 0. Lineage variant required at
Step 1 for any picked species (purebred or per-hybrid-parent) with
VariantAxis == "lineage".

Aside: AddVariantContent layers the resolved variant's extra
traits/detriments onto the base species rendering, for both purebred
and hybrid paths.

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

Theriapolis.Godot/Scenes/Steps/StepClade.cs

@@ -22,6 +22,8 @@ public partial class StepClade : VBoxContainer, IStep
 {
     private CharacterDraft _draft = null!;
     private Button _hybridToggle = null!;
+    private Button _sexMaleBtn = null!;
+    private Button _sexFemaleBtn = null!;
     private VBoxContainer _purebredSection = null!;
     private VBoxContainer _hybridSection = null!;
     private OptionButton _dominantToggle = null!;
@@ -83,6 +85,27 @@ public partial class StepClade : VBoxContainer, IStep
             AutowrapMode = TextServer.AutowrapMode.WordSmart,
         });
 
+        // Sex picker — required for every character. For purebreds with
+        // sex-axis variants (Elk, Lion) this drives variant resolution;
+        // for hybrids it's identity-only since sire/dam are male/female
+        // by parent-role definition.
+        var sexRow = new HBoxContainer();
+        sexRow.AddThemeConstantOverride("separation", 8);
+        AddChild(sexRow);
+        sexRow.AddChild(new Label { Text = "SEX", ThemeTypeVariation = "Eyebrow" });
+        _sexMaleBtn = new Button
+        {
+            Text = "Male", ToggleMode = true, FocusMode = Control.FocusModeEnum.None,
+        };
+        _sexFemaleBtn = new Button
+        {
+            Text = "Female", ToggleMode = true, FocusMode = Control.FocusModeEnum.None,
+        };
+        _sexMaleBtn.Pressed   += () => OnSexPicked("male");
+        _sexFemaleBtn.Pressed += () => OnSexPicked("female");
+        sexRow.AddChild(_sexMaleBtn);
+        sexRow.AddChild(_sexFemaleBtn);
+
         // Toggle Button (not CheckBox) so the inverted-on-press button style
         // from the codex theme handles selection visually — no checkbox glyph
         // needed, the bg colour shift is the affordance.
@@ -224,6 +247,9 @@ public partial class StepClade : VBoxContainer, IStep
         _draft.Patch(patch);
     }
 
+    private void OnSexPicked(string sex) =>
+        _draft.Patch(new Godot.Collections.Dictionary { { "sex", sex } });
+
     private void OnDominantSelected(long index)
     {
         string newDominant = index == 0 ? "sire" : "dam";
@@ -259,6 +285,11 @@ public partial class StepClade : VBoxContainer, IStep
         _purebredSection.Visible = !hybrid;
         _hybridSection.Visible = hybrid;
 
+        bool isMale   = _draft.Sex == "male";
+        bool isFemale = _draft.Sex == "female";
+        if (_sexMaleBtn.ButtonPressed   != isMale)   _sexMaleBtn.SetPressedNoSignal(isMale);
+        if (_sexFemaleBtn.ButtonPressed != isFemale) _sexFemaleBtn.SetPressedNoSignal(isFemale);
+
         UpdateSelection(_purebredCards, _draft.CladeId);
         UpdateSelection(_sireCards, _draft.SireCladeId);
         UpdateSelection(_damCards, _draft.DamCladeId);