M6.17: Variant content + Sheep/Goat split + calling lore + uniform card layout

Species variants populated against the M6.13 schema:
- Lion-Folk sex axis: Mane Guard (male) / Huntress Reflexes (female,
  +5 ft speed + advantage on initiative).
- Elk-Folk sex axis: Antler Combat with 10 ft reach when full rack
  (male, retains seasonal Antler Drag) / Kick (female, prone on crit).
  Base traits restored to doc canon: Herd Coordination (Help → +3) +
  Endurance Runner (40 ft + advantage CON vs forced march); base speed
  bumped 30 → 40; new base detriment Herd Instinct.

Ram-Folk replaced with separate Sheep-Folk + Goat-Folk species rather
than a lineage-axis variant on a single Ram entry. Bovidae now has 4
species. The lineage-axis toggle UI in StepSpecies BuildCard rolled
back; the schema stays for sex-axis (Lion/Elk) which auto-resolves.
ContentLoadTests + HybridCharacterTests updated; Size.cs comment too.

Calling lore: ClassDef gains Description; classes.json populated for
all 8 callings with the doc's italic blockquote + paragraph profile.
StepClass surfaces the description on the card.

Card layout uniformity: StepClass / StepSubclass / StepBackground all
switched to single-column ExpandFill grids (matching StepClade /
StepSpecies). Each card now spans the wizard's content width so the
description and feature chips have room to breathe.

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

Theriapolis.Godot/Scenes/Steps/StepBackground.cs

@@ -43,9 +43,8 @@ public partial class StepBackground : VBoxContainer, IStep
             AutowrapMode = TextServer.AutowrapMode.WordSmart,
         });
 
-        _grid = new GridContainer { Columns = 3, SizeFlagsHorizontal = SizeFlags.ShrinkCenter };
-        _grid.AddThemeConstantOverride("h_separation", 16);
-        _grid.AddThemeConstantOverride("v_separation", 16);
+        _grid = new GridContainer { Columns = 1, SizeFlagsHorizontal = SizeFlags.ExpandFill };
+        _grid.AddThemeConstantOverride("v_separation", 12);
         AddChild(_grid);
 
         Refresh();
@@ -67,7 +66,7 @@ public partial class StepBackground : VBoxContainer, IStep
         bool selected = _draft.BackgroundId == bg.Id;
 
         var card = CodexCard.Make();
-        card.CustomMinimumSize = new Vector2(200, 0);
+        card.SizeFlagsHorizontal = Control.SizeFlags.ExpandFill;
         CodexCard.SetSelected(card, selected);
 
         card.GuiInput += (InputEvent e) =>