fix: preserve position during SE/S/E resize to prevent rounding drift

During resize events, _dragOrResize unconditionally recalculates x/y
from pixel positions for all handle directions. For SE/S/E handles,
the top-left corner is anchored and should never move. The pixel→grid
round-trip through Math.round() introduces rounding errors that cause
position drift, especially on fine grids with small cell sizes (e.g.
column:480, cellHeight:'0.38vh' ≈ 3.5px per cell).

This fix:
- Passes the resize handle direction (dir) from DDResizable._resizing()
  through the event object as event.resizeDir
- In _dragOrResize, only recalculates x/y when the handle moves the
  top-left corner (contains 'n' or 'w')
- For SE/S/E handles, preserves the original position from node._orig

Since p is initialized from { ...node._orig }, x/y naturally keep their
original values when not overwritten.

Fixes #385, relates to #811, #1356

Author: KokXinTan

src/dd-resizable.ts

@@ -184,6 +184,7 @@ export class DDResizable extends DDBaseImplement implements HTMLElementExtendOpt
     this.temporalRect = this._getChange(event, dir);
     this._applyChange();
     const ev = Utils.initEvent<MouseEvent>(event, { type: 'resize', target: this.el });
+    (ev as any).resizeDir = dir; // expose handle direction so _dragOrResize can avoid position drift
     if (this.option.resize) {
       this.option.resize(ev, this._ui());
     }

src/gridstack.ts

@@ -2928,11 +2928,16 @@ export class GridStack {
       if (node.w === p.w && node.h === p.h) return;
       if (node._lastTried && node._lastTried.w === p.w && node._lastTried.h === p.h) return; // skip one we tried (but failed)
 
-      // if we size on left/top side this might move us, so get possible new position as well
-      const left = ui.position.left + mLeft;
-      const top = ui.position.top + mTop;
-      p.x = Math.round(left / cellWidth);
-      p.y = Math.round(top / cellHeight);
+      // only recalculate position for handles that move the top-left corner (N/W).
+      // for SE/S/E handles the top-left is anchored — recalculating from pixels causes
+      // rounding drift on fine grids where cellWidth/cellHeight are only a few pixels. #385 #1356
+      const dir = ((event as any).resizeDir || '') as string;
+      if (dir.includes('w') || dir.includes('n')) {
+        const left = ui.position.left + mLeft;
+        const top = ui.position.top + mTop;
+        if (dir.includes('w')) p.x = Math.round(left / cellWidth);
+        if (dir.includes('n')) p.y = Math.round(top / cellHeight);
+      }
 
       resizing = true;
     }