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/World/FactionInfluence.cs

@@ -0,0 +1,50 @@
+namespace Theriapolis.Core.World;
+
+public enum FactionId : byte
+{
+    CovenantEnforcers = 0,
+    Inheritors        = 1,
+    ThornCouncil      = 2,
+}
+
+/// <summary>
+/// Per-tile influence map for the three primary factions.
+/// Influence[factionIndex, x, y] ∈ [0, 1].
+/// </summary>
+public sealed class FactionInfluenceMap
+{
+    public const int FactionCount = 3;
+
+    // Flat array: [faction * W * H + y * W + x]
+    private readonly float[] _data;
+    private const int W = C.WORLD_WIDTH_TILES;
+    private const int H = C.WORLD_HEIGHT_TILES;
+
+    public FactionInfluenceMap()
+    {
+        _data = new float[FactionCount * W * H];
+    }
+
+    public float Get(int faction, int x, int y) => _data[faction * W * H + y * W + x];
+    public void  Set(int faction, int x, int y, float value) =>
+        _data[faction * W * H + y * W + x] = value;
+
+    public void Add(int faction, int x, int y, float delta)
+    {
+        int idx = faction * W * H + y * W + x;
+        _data[idx] = Math.Max(0f, Math.Min(1f, _data[idx] + delta));
+    }
+
+    /// <summary>Returns the index of the faction with highest influence at this tile, or -1 if all zero.</summary>
+    public int DominantFaction(int x, int y)
+    {
+        float best = 0f;
+        int idx = -1;
+        for (int f = 0; f < FactionCount; f++)
+        {
+            float v = Get(f, x, y);
+            if (v > best) { best = v; idx = f; }
+        }
+        return idx;
+    }
+}