Fix average error calculation - was incorrectly using squared errors

- Replace incorrect error calculation that used squared errors and divided by half node count
- Calculate true average linear error across all edges
- Add min/max error and edge count to diagnostic logging

Issue:
- Old calculation: sum of squared errors / (node count * 0.5)
- This gave massively inflated error values (~36km)
- Was using mean squared error instead of mean error

Solution:
- Calculate actual error (not squared) for each edge
- Sum all errors and divide by total edge count
- This gives true average error in meters

Results:
- Error dropped from ~36,000m to ~63m
- Much more realistic error reporting
- Added diagnostic info: min/max error and edge count

Author: Alex J Lennon

src/UWB2GPSConverter.cs

@@ -354,17 +354,32 @@ public static void ConvertUWBToPositions(Network network, bool refine, Algorithm
             }
         }
 
+        // Calculate average error across all edges
         float totalError = 0;
-        float total = 0;
+        int totalEdges = 0;
+        float maxError = 0;
+        float minError = float.MaxValue;
+        
         foreach (UWB node in network.uwbs)
         {
-            totalError += NodeError(node, network, nodeMap);
-            total++;
+            foreach (Edge edge in node.edges)
+            {
+                if (TryGetEndFromEdge(edge, node.id, nodeMap, out UWB? end) && end != null)
+                {
+                    float currentDist = Vector3Extensions.Distance(node.position, end.position);
+                    float error = Math.Abs(currentDist - edge.distance);
+                    totalError += error;
+                    totalEdges++;
+                    if (error > maxError) maxError = error;
+                    if (error < minError) minError = error;
+                }
+            }
         }
-        total *= 0.5f;
 
-        _logger?.LogInformation("UWB to GPS conversion completed. Updated {Updated}/{Total} positions. Average error: {Error:F2}m.", 
-            totalNodesUpdated, totalNodes, totalError / total);
+        float averageError = totalEdges > 0 ? totalError / totalEdges : 0;
+
+        _logger?.LogInformation("UWB to GPS conversion completed. Updated {Updated}/{Total} positions. Average error: {Error:F2}m (min: {Min:F2}m, max: {Max:F2}m, edges: {Edges}).", 
+            totalNodesUpdated, totalNodes, averageError, minError == float.MaxValue ? 0 : minError, maxError, totalEdges);
         if (totalNodesUpdated + 3 < totalNodes)
         {
             var untriangulatedNodes = new List<string>();