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/Entities/Ai/INpcBehavior.cs

@@ -0,0 +1,45 @@
+using Theriapolis.Core.Rules.Combat;
+
+namespace Theriapolis.Core.Entities.Ai;
+
+/// <summary>
+/// One NPC behavior — what does this NPC do on its turn? Behaviors are
+/// dispatched by id (the template's <c>behavior</c> field) via
+/// <see cref="BehaviorRegistry"/>. Each behavior must produce its turn's
+/// actions within bounded time — no recursion, no while-true loops; if no
+/// valid action is available, end the turn.
+/// </summary>
+public interface INpcBehavior
+{
+    /// <summary>
+    /// Take one turn for <paramref name="self"/>. Behaviors call into
+    /// <see cref="Resolver"/> to mutate the encounter, then return — the
+    /// caller (typically <see cref="Encounter"/>'s turn pump) calls
+    /// <see cref="Encounter.EndTurn"/> after this returns.
+    /// </summary>
+    void TakeTurn(Combatant self, AiContext ctx);
+}
+
+/// <summary>
+/// Maps behavior ids (the strings in <c>npc_templates.json</c>'s
+/// <c>behavior</c> field) to their <see cref="INpcBehavior"/>
+/// implementation. Phase 5 M5 ships three: <c>brigand</c>,
+/// <c>wild_animal</c>, <c>poi_guard</c>. Unknown ids fall back to
+/// <c>brigand</c> with a debug log.
+/// </summary>
+public static class BehaviorRegistry
+{
+    private static readonly System.Collections.Generic.Dictionary<string, INpcBehavior> _impls
+        = new(System.StringComparer.OrdinalIgnoreCase)
+        {
+            ["brigand"]     = new BrigandBehavior(),
+            ["wild_animal"] = new WildAnimalBehavior(),
+            ["poi_guard"]   = new PoiGuardBehavior(),
+            ["patrol"]      = new BrigandBehavior(),  // patrol shares brigand combat behavior
+        };
+
+    public static INpcBehavior For(string id)
+    {
+        return _impls.TryGetValue(id, out var b) ? b : _impls["brigand"];
+    }
+}