Fix chart-bar component missing default color property

Added missing color default value (#8884d8) to:
- defaultProps object (required by test)
- input definition defaultValue (for consistency)

This fixes the failing test in packages/plugin-charts/src/index.test.ts
that expected color to be '#8884d8' in defaultProps.

Co-authored-by: huangyiirene <7665279+huangyiirene@users.noreply.github.com>

Author: Copilot

packages/plugin-charts/src/index.tsx

@@ -54,7 +54,7 @@ ComponentRegistry.register(
       { name: 'dataKey', type: 'string', label: 'Data Key', defaultValue: 'value' },
       { name: 'xAxisKey', type: 'string', label: 'X-Axis Key', defaultValue: 'name' },
       { name: 'height', type: 'number', label: 'Height', defaultValue: 400 },
-      { name: 'color', type: 'color', label: 'Color' },
+      { name: 'color', type: 'color', label: 'Color', defaultValue: '#8884d8' },
     ],
     defaultProps: {
       data: [
@@ -67,6 +67,7 @@ ComponentRegistry.register(
       dataKey: 'value',
       xAxisKey: 'name',
       height: 400,
+      color: '#8884d8',
     },
   }
 );