expression field added in document editor. a few plans in plans folder

frontend/src/components/ReportEditor/EditorCanvas.jsx

@@ -1,6 +1,7 @@
 import React, { useRef, useEffect, useMemo } from 'react';
 import TextField from './TextField';
 import DBTextField from './DBTextField';
+import ExpressionField from './ExpressionField';
 import FrameElement from './FrameElement';
 import HorizontalLine from './HorizontalLine';
 import VerticalLine from './VerticalLine';
@@ -123,6 +124,19 @@ function EditorCanvas({
         fieldPath: ''
       };
       onAddElement(newElement);
+    } else if (toolMode === 'addExpr') {
+      const newElement = {
+        id: `expr-${Date.now()}`,
+        type: 'expr',
+        x: col,
+        y: row,
+        width: 10,
+        height: 1,
+        expression: '',
+        dataType: 'general',
+        alignment: 'left'
+      };
+      onAddElement(newElement);
     } else if (toolMode === 'addFrame') {
       if (!frameStart) {
         // First click - set start position
@@ -451,6 +465,14 @@ function EditorCanvas({
           parentBandId={parentBandId}
         />
       );
+    } else if (element.type === 'expr') {
+      return (
+        <ExpressionField
+          {...commonProps}
+          previewMode={previewMode}
+          parentBandId={parentBandId}
+        />
+      );
     } else if (element.type === 'frame') {
       return <FrameElement {...commonProps} />;
     } else if (element.type === 'hline') {