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/Quests/QuestState.cs

@@ -0,0 +1,30 @@
+namespace Theriapolis.Core.Rules.Quests;
+
+/// <summary>
+/// Phase 6 M4 — runtime per-quest state. One instance per active or
+/// completed quest. The <see cref="QuestEngine"/> looks up the parent
+/// <see cref="Data.QuestDef"/> by id when ticking, so this struct stays
+/// small and serialises cleanly into the save layer.
+/// </summary>
+public sealed class QuestState
+{
+    public string         QuestId      { get; init; } = "";
+    public string         CurrentStep  { get; set; } = "";
+    public QuestStatus    Status       { get; set; } = QuestStatus.Active;
+
+    /// <summary>WorldClock seconds when the quest started.</summary>
+    public long           StartedAt    { get; set; }
+
+    /// <summary>WorldClock seconds when the current step entered.</summary>
+    public long           StepStartedAt { get; set; }
+
+    /// <summary>Free-form journal entries the player can browse from QuestLog.</summary>
+    public List<string>   Journal      { get; } = new();
+}
+
+public enum QuestStatus : byte
+{
+    Active    = 0,
+    Completed = 1,
+    Failed    = 2,
+}