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/Items/SizeMatch.cs

@@ -0,0 +1,49 @@
+using Theriapolis.Core.Data;
+using Theriapolis.Core.Rules.Stats;
+
+namespace Theriapolis.Core.Items;
+
+/// <summary>
+/// Body-size compatibility check for equipment. Per equipment.md:
+///   "Most equipment comes in Small, Medium, and Large variants. Using
+///    equipment not sized for your body imposes disadvantage on relevant
+///    checks unless it has the Adaptive property."
+///
+/// Returns <see cref="MatchResult.Match"/> when the item lists the wearer's
+/// size, <see cref="MatchResult.Adaptive"/> when not listed but the item has
+/// the "adaptive" property (no penalty), and
+/// <see cref="MatchResult.WrongSize"/> otherwise (wearer takes disadvantage).
+/// </summary>
+public static class SizeMatch
+{
+    public enum MatchResult : byte
+    {
+        Match     = 0,  // item explicitly fits the wearer's size
+        Adaptive  = 1,  // item is universally adaptive — no disadvantage
+        WrongSize = 2,  // wearer can equip it but suffers disadvantage
+    }
+
+    public static MatchResult Check(ItemDef def, SizeCategory wearerSize)
+    {
+        string wearerKey = wearerSize switch
+        {
+            SizeCategory.Tiny        => "tiny",
+            SizeCategory.Small       => "small",
+            SizeCategory.Medium      => "medium",
+            SizeCategory.MediumLarge => "medium",   // M-Large uses Medium-sized gear
+            SizeCategory.Large       => "large",
+            SizeCategory.Huge        => "large",    // closest available
+            _ => "medium",
+        };
+
+        foreach (var s in def.Sizes)
+            if (string.Equals(s, wearerKey, StringComparison.OrdinalIgnoreCase))
+                return MatchResult.Match;
+
+        foreach (var p in def.Properties)
+            if (string.Equals(p, "adaptive", StringComparison.OrdinalIgnoreCase))
+                return MatchResult.Adaptive;
+
+        return MatchResult.WrongSize;
+    }
+}