feat: add cursor circle visual feedback during line drawing (Phase 2)

LINE_DRAWING_IMPROVEMENTS.md

@@ -78,7 +78,7 @@ stroke={annotation.color || '#3b82f6'}
 
 ---
 
-### Phase 2: Visual Feedback
+### Phase 2: Visual Feedback ✅ DONE
 
 #### 2.1 Cursor Circle During Drawing
 **File**: `src/components/SvgOverlay.tsx`

src/components/SvgOverlay.tsx

@@ -334,6 +334,22 @@ export default function SvgOverlay({
     );
   };
 
+  // Render cursor circle during line drawing
+  const renderCursorCircle = () => {
+    if (!drawingLine || !mousePosition) return null;
+
+    return (
+      <circle
+        cx={mousePosition.x}
+        cy={mousePosition.y}
+        r={5}
+        fill="transparent"
+        stroke={selectedColor}
+        strokeWidth={2}
+      />
+    );
+  };
+
   if (!chart || !series) return null;
 
   return (
@@ -354,6 +370,7 @@ export default function SvgOverlay({
     >
       {renderLines()}
       {renderPreviewLine()}
+      {renderCursorCircle()}
     </svg>
   );
 }