fix(refboard): dot grid behind canvas, paste at native size

- Make PixiJS canvas background transparent so SVG dot grid shows through
- Move dot grid SVG before canvas in DOM with zIndex 0 (behind images)
- Set wrapper div background to #1e1e1e
- Remove 600px cap on pasted images — preserve native dimensions

frontend/src/pages/Editor.tsx

@@ -468,16 +468,8 @@ export default function Editor({ isPublicView }: EditorProps) {
       />}
 
       {/* Canvas */}
-      <div style={{ flex: 1, position: 'relative', overflow: 'hidden' }} onContextMenu={handleContextMenu}>
-        <PixiCanvas
-          ref={canvasRef}
-          canvasState={canvasState}
-          currentTool={activeTool}
-          boardId={resolvedBoardId}
-          onChange={onCanvasChange}
-        />
-
-        {/* Dot grid — above canvas, below UI, no pointer events */}
+      <div style={{ flex: 1, position: 'relative', overflow: 'hidden', background: '#1e1e1e' }} onContextMenu={handleContextMenu}>
+        {/* Dot grid — behind transparent canvas */}
         {showGrid && (() => {
           const scale = canvasTransform[0] || 1;
           const tx = canvasTransform[4] || 0;
@@ -491,7 +483,7 @@ export default function Editor({ isPublicView }: EditorProps) {
           const oy = ty % screenSpacing;
           const alpha = Math.max(0.12, Math.min(0.35, scale * 0.18));
           return (
-            <svg style={{ position: 'absolute', inset: 0, pointerEvents: 'none', zIndex: 1 }} width="100%" height="100%">
+            <svg style={{ position: 'absolute', inset: 0, pointerEvents: 'none', zIndex: 0 }} width="100%" height="100%">
               <defs>
                 <pattern id="dotgrid" width={screenSpacing} height={screenSpacing} patternUnits="userSpaceOnUse" x={ox} y={oy}>
                   <circle cx={dotR} cy={dotR} r={dotR} fill={`rgba(255,255,255,${alpha})`} />
@@ -501,6 +493,14 @@ export default function Editor({ isPublicView }: EditorProps) {
             </svg>
           );
         })()}
+        <PixiCanvas
+          ref={canvasRef}
+          canvasState={canvasState}
+          currentTool={activeTool}
+          boardId={resolvedBoardId}
+          onChange={onCanvasChange}
+        />
+
 
         <UserCursors
           socket={getSocket()}