fix(super-editor): align image resize handles with actual image position (#2293)

The ImageResizeOverlay calculates coordinates relative to .super-editor
(via closest('.super-editor')), but .super-editor had no position set.
The overlay's position:absolute resolved to .super-editor-container
instead, causing a coordinate mismatch whenever there was any offset
between the two (e.g., a ruler above the editor).

Add position:relative to .super-editor so it becomes the positioned
ancestor that matches the overlay's coordinate math.

Author: tupizz

packages/super-editor/src/components/SuperEditor.vue

@@ -1262,6 +1262,7 @@ onBeforeUnmount(() => {
 .super-editor {
   color: initial;
   overflow: hidden;
+  position: relative;
 }
 
 .placeholder-editor {