fix(canvas): ensure icon selection box is always square with centered content

For icon nodes (PathNode with iconId), expand Fabric's logical bounding box to
the declared w×h so selection handles always form a perfect square, while the
path content remains centered via Fabric's natural pathOffset.

src/canvas/canvas-object-factory.ts

@@ -320,7 +320,14 @@ export function createFabricObject(
       if (pw > 0 && ph > 0 && obj.width && obj.height) {
         // Uniform scale — preserve aspect ratio so icons don't get squished
         const uniformScale = Math.min(pw / obj.width, ph / obj.height)
-        obj.set({ scaleX: uniformScale, scaleY: uniformScale })
+        if (node.iconId) {
+          // For icon nodes: expand the Fabric bounding box to pw×ph so the selection
+          // handles always form a perfect square. The path content is naturally centered
+          // by Fabric's pathOffset (center of path's bbox).
+          obj.set({ width: pw / uniformScale, height: ph / uniformScale, scaleX: uniformScale, scaleY: uniformScale })
+        } else {
+          obj.set({ scaleX: uniformScale, scaleY: uniformScale })
+        }
       }
       break
     }

src/canvas/canvas-object-sync.ts

@@ -187,7 +187,13 @@ export function syncFabricObject(
         if (node.type === 'path') {
           // Uniform scale — preserve aspect ratio so icons don't get squished
           const uniformScale = Math.min(w / nw, h / nh)
-          obj.set({ width: nw, height: nh, scaleX: uniformScale, scaleY: uniformScale })
+          if (node.iconId) {
+            // Expand bounding box to w×h so selection handles form a perfect square.
+            // Path content is centered automatically by Fabric's pathOffset.
+            obj.set({ width: w / uniformScale, height: h / uniformScale, scaleX: uniformScale, scaleY: uniformScale })
+          } else {
+            obj.set({ width: nw, height: nh, scaleX: uniformScale, scaleY: uniformScale })
+          }
         } else {
           obj.set({ width: nw, height: nh, scaleX: w / nw, scaleY: h / nh })
         }