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/Rules/Combat/Turn.cs

@@ -0,0 +1,38 @@
+namespace Theriapolis.Core.Rules.Combat;
+
+/// <summary>
+/// Mutable per-turn state for the active combatant: action / bonus action /
+/// reaction availability and remaining movement budget. The
+/// <see cref="Encounter"/> rebuilds this when each new turn begins; the
+/// <see cref="Resolver"/> consumes resources as the combatant uses them.
+///
+/// Phase 5 M4 tracks the booleans but doesn't enforce them inside Resolver
+/// (callers can attack twice in a turn if they want — useful for tests).
+/// M5 introduces per-action-cost gating in the live PlayScreen wrapper.
+/// </summary>
+public struct Turn
+{
+    public int  CombatantId;
+    public bool ActionAvailable;
+    public bool BonusActionAvailable;
+    public bool ReactionAvailable;
+    public int  RemainingMovementFt;
+
+    public static Turn FreshFor(int combatantId, int speedFt) => new()
+    {
+        CombatantId          = combatantId,
+        ActionAvailable      = true,
+        BonusActionAvailable = true,
+        ReactionAvailable    = true,
+        RemainingMovementFt  = speedFt,
+    };
+
+    public void ConsumeAction()      => ActionAvailable      = false;
+    public void ConsumeBonusAction() => BonusActionAvailable = false;
+    public void ConsumeReaction()    => ReactionAvailable    = false;
+    public void ConsumeMovement(int feet)
+    {
+        RemainingMovementFt -= feet;
+        if (RemainingMovementFt < 0) RemainingMovementFt = 0;
+    }
+}