v0.0.3 - Gradient Rendering & API Improvements

What's New

• Gradient Links - Smooth color transitions between source and target nodes using LinearGradient shaders
• Texture Overlay - Optional subtle patterns on links for enhanced visual depth
• HSL Selection Borders - Contrasting borders on selected nodes using intelligent color manipulation
• Type Safety - Strongly typed SankeyLink.source and SankeyLink.target as SankeyNode
• Improved API - New onNodeSelected(SankeyNode?) callback with full node object access
• Responsive Example - Demo app with LayoutBuilder for adaptive sizing

Enhancements

• Renamed node position fields from x0/x1/y0/y1 to left/right/top/bottom for clarity
• Added SankeyNode.displayLabel getter that returns label or falls back to id.toString()
• Added SankeyNode.contains(Offset) method for cleaner tap detection
• Fixed shouldRepaint to properly trigger repaints when showLabels or showTexture change
• Added comprehensive widget tests

Breaking Changes

• Removed deprecated onNodeTap(int?) callback. Use onNodeSelected(SankeyNode?) instead.

Thanks to @jheyne for the gradient rendering contribution!