Toroidal world: boundless wrapping globe, 2x2 even town grid

The map is now a torus - walk off any edge and reappear on the opposite
side, no edges or corners. A new Toroidal helper carries all wrap-aware
distance/direction/movement math, and every position comparison in the sim
routes through it: soul pressure, node + structure sensing, gift/teacher/
neighbor scans, bonding, movement, the spatial grids (NPC and node cell
index both wrap their bucket lookups at the seam), and town centroid
(averaged in anchor-relative deltas, since averaging raw coordinates across
the seam is meaningless).

Towns re-laid as a 2x2 even grid on the torus (quarter/three-quarter points,
320 & 960 on a 1280 world): every town sits exactly 640 units from each of
its two axis-neighbours in all directions, wrap included - no more edge-boxed
North/South that could only forage inward. World grew 1152 -> 1280 with
resources scaled to area.

Verified over a 240-day soak: all four towns alive and balanced (pop 23-25),
population stable ~96, 119 bonds (27 cross-town), cultures still diverge, and
wrapped distances correctly cap at the torus half-diagonal (no false
across-seam blowups). 183s headless.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/SpatialGrid.cs

@@ -41,11 +41,16 @@ public class SpatialGrid
     public void ForEachNear(Vector2 center, float radius, System.Action<Npc> action)
     {
         int reach = Mathf.CeilToInt(radius / _cell);
+        int cols = Mathf.CeilToInt(Toroidal.Size / _cell);   // buckets per axis
         var (cx, cy) = Key(center);
+        // Wrap bucket coordinates so a search near the seam also scans the
+        // buckets on the far edge — the world is a torus.
         for (int dx = -reach; dx <= reach; dx++)
         for (int dy = -reach; dy <= reach; dy++)
         {
-            if (_buckets.TryGetValue((cx + dx, cy + dy), out var list))
+            int gx = ((cx + dx) % cols + cols) % cols;
+            int gy = ((cy + dy) % cols + cols) % cols;
+            if (_buckets.TryGetValue((gx, gy), out var list))
                 foreach (var npc in list) action(npc);
         }
     }