fix(canvas): snap whole-line drag and guard image div-by-zero

LineObject's whole-line onDragMove only updated dragDelta with the
raw cursor delta — the endpoint handles in the same component snap,
and the rest of the canvas snaps too, so the inconsistency was
visible. Mirror the endpoint idiom: round-trip pixel → dot → snap →
pixel, then update both Konva position and the React state.

ImageObject divided cached.height by cached.width to compute aspect
ratio. A 0-width image would yield NaN. Guard with width > 0; falls
back to a square placeholder.

Author: u8array

src/components/Canvas/ImageObject.tsx

@@ -27,7 +27,12 @@ export function ImageObject({
   const p = obj.props;
   const cached = getImage(p.imageId);
   const w = dotsToPx(p.widthDots, scale, dpmm);
-  const h = cached ? w * (cached.height / cached.width) : w;
+  // Guard against a 0-width cached image: the imageCache pipeline
+  // doesn't normally produce one, but a malformed file could leak
+  // through and div-by-zero would render NaN-sized canvas nodes.
+  const h = cached && cached.width > 0
+    ? w * (cached.height / cached.width)
+    : w;
   const x = offsetX + dotsToPx(obj.x, scale, dpmm);
   const y = offsetY + dotsToPx(obj.y, scale, dpmm);
 

src/components/Canvas/LineObject.tsx

@@ -86,7 +86,15 @@ export function LineObject({
         }
         onTap={() => onSelect(false)}
         onDragMove={(e) => {
-          setDragDelta({ x: e.target.x(), y: e.target.y() });
+          // Snap the whole-line delta in dot space, then mirror back
+          // to pixels — same idiom the endpoint handles use, and
+          // keeps the line consistent with shape/text/image drag.
+          const deltaXPx =
+            dotsToPx(snap(pxToDots(e.target.x(), scale, dpmm)), scale, dpmm);
+          const deltaYPx =
+            dotsToPx(snap(pxToDots(e.target.y(), scale, dpmm)), scale, dpmm);
+          e.target.position({ x: deltaXPx, y: deltaYPx });
+          setDragDelta({ x: deltaXPx, y: deltaYPx });
         }}
         onDragEnd={(e) => {
           const deltaXPx = e.target.x();