fix: dragging now switches source unit to update all bars correctly

Fixed dragging behavior so all bars update when you drag:

Problem:
- Dragging a bar would change values but bars wouldn't visually update
- The bar would reset to original length on release
- Other bars wouldn't change at all

Root cause:
- We were converting the dragged value back to the selected unit
- This kept the source unit the same, so relative percentages didn't change
- The logarithmic scale maintained proportions, preventing visual updates

Solution:
- When dragging a bar, switch to that unit as the new source unit
- Set both inputValue and selectedUnit to the dragged unit's value/name
- This changes the conversion base, making all other bars recalculate
- Removed draggedPercentage state (not needed with this approach)
- All bars now use calculated percentages from conversions

How it works now:
- Drag the "feet" bar → becomes the source unit (selectedUnit = 'ft')
- All conversions recalculate from feet
- All bars update their percentages based on new conversion base
- No transitions during drag for instant visual feedback
- Smooth animation when drag ends

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/converter/MainConverter.tsx

@@ -125,11 +125,10 @@ export default function MainConverter() {
 
   // Handle value change from draggable bars
   const handleValueChange = useCallback((value: number, unit: string) => {
-    // Convert the dragged unit's value back to the currently selected unit
-    const convertedValue = convertUnit(value, unit, selectedUnit);
-    setInputValue(convertedValue.toString());
-    // Keep selectedUnit the same - user is still inputting in that unit
-  }, [selectedUnit]);
+    // When dragging a bar, switch to that unit as the source
+    setInputValue(value.toString());
+    setSelectedUnit(unit);
+  }, []);
 
   return (
     <div className="w-full max-w-6xl mx-auto space-y-6">