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/Persistence/QuestSnapshot.cs

@@ -0,0 +1,25 @@
+namespace Theriapolis.Core.Persistence;
+
+/// <summary>
+/// Phase 6 M4 — serializable quest engine state. Holds active + completed
+/// quests + the player journal tail. Round-trips via SaveCodec
+/// <c>TAG_QUESTS = 111</c>.
+/// </summary>
+public sealed class QuestSnapshot
+{
+    public List<QuestStateSnapshot> Active    { get; set; } = new();
+    public List<QuestStateSnapshot> Completed { get; set; } = new();
+
+    /// <summary>Most recent journal entries written by the engine.</summary>
+    public List<string> Journal { get; set; } = new();
+}
+
+public sealed class QuestStateSnapshot
+{
+    public string QuestId       { get; set; } = "";
+    public string CurrentStep   { get; set; } = "";
+    public byte   Status        { get; set; }     // QuestStatus byte value
+    public long   StartedAt     { get; set; }
+    public long   StepStartedAt { get; set; }
+    public string[] JournalLines { get; set; } = System.Array.Empty<string>();
+}