Initial commit: Theriapolis baseline at port/godot branch point

Captures the pre-Godot-port state of the codebase. This is the rollback
anchor for the Godot port (M0 of theriapolis-rpg-implementation-plan-godot-port.md).
All Phase 0 through Phase 6.5 work is included; Phase 7 is in flight.

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

Theriapolis.Core/Data/SpeciesDef.cs

@@ -0,0 +1,38 @@
+using System.Text.Json.Serialization;
+
+namespace Theriapolis.Core.Data;
+
+/// <summary>
+/// Immutable species (subrace-equivalent) record loaded from species.json.
+/// Refines the parent <see cref="CladeDef"/>: adds a body size, additional
+/// ability mods, species-specific traits, and species-specific detriments.
+/// </summary>
+public sealed record SpeciesDef
+{
+    [JsonPropertyName("id")]
+    public string Id { get; init; } = "";
+
+    [JsonPropertyName("clade_id")]
+    public string CladeId { get; init; } = "";
+
+    [JsonPropertyName("name")]
+    public string Name { get; init; } = "";
+
+    /// <summary>Body size category, snake_case (small / medium / medium_large / large).</summary>
+    [JsonPropertyName("size")]
+    public string Size { get; init; } = "medium";
+
+    /// <summary>Additional ability mods on top of the clade's mods.</summary>
+    [JsonPropertyName("ability_mods")]
+    public Dictionary<string, int> AbilityMods { get; init; } = new();
+
+    /// <summary>Base movement speed in feet per turn (5 ft. = 1 tactical tile per d20 standard).</summary>
+    [JsonPropertyName("base_speed_ft")]
+    public int BaseSpeedFt { get; init; } = 30;
+
+    [JsonPropertyName("traits")]
+    public TraitDef[] Traits { get; init; } = Array.Empty<TraitDef>();
+
+    [JsonPropertyName("detriments")]
+    public TraitDef[] Detriments { get; init; } = Array.Empty<TraitDef>();
+}