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/Actor.cs

@@ -0,0 +1,45 @@
+using Theriapolis.Core.Rules.Character;
+using Theriapolis.Core.Util;
+
+namespace Theriapolis.Core.Entities;
+
+/// <summary>
+/// Base actor record. Position is in world-pixel space and is meaningful in
+/// both the world-map view and the tactical view (see Section 5 of the
+/// implementation plan — one canonical coordinate system).
+///
+/// Phase 5 adds the optional <see cref="Character"/> attachment carrying all
+/// gameplay state (stats, inventory, HP, conditions). The renderer layer
+/// stays ignorant of the gameplay layer — Camera2D doesn't need to know HP.
+/// </summary>
+public class Actor
+{
+    /// <summary>Stable id assigned by <see cref="ActorManager"/>.</summary>
+    public int Id { get; init; }
+
+    /// <summary>World-pixel position. Reused at both zoom scales.</summary>
+    public Vec2 Position { get; set; }
+
+    /// <summary>Facing angle in radians (0 = east, π/2 = south).</summary>
+    public float FacingAngleRad { get; set; }
+
+    /// <summary>Continuous-time travel speed on the world map, in world pixels per real second.</summary>
+    public float SpeedWorldPxPerSec { get; set; } = C.PLAYER_TRAVEL_PX_PER_SEC;
+
+    /// <summary>
+    /// Phase 5: gameplay state. Null when this actor isn't combat-capable
+    /// (cosmetic NPCs, future-phase additions). PlayerActor and NpcActor
+    /// always carry one.
+    /// </summary>
+    public Character? Character { get; set; }
+
+    /// <summary>Whose side this actor is on. Drives encounter triggering and AI targeting.</summary>
+    public Allegiance Allegiance { get; set; } = Allegiance.Neutral;
+
+    /// <summary>
+    /// True if this actor still has positive HP (or is downed but not dead).
+    /// Subclasses (e.g. <see cref="NpcActor"/>) override to use direct HP
+    /// fields instead of a <see cref="Character"/> reference.
+    /// </summary>
+    public virtual bool IsAlive => Character is null ? true : Character.IsAlive;
+}