feat(bar): support per-bar color palettes in playground

[hdcodedev]

Why

The playground could configure only a single barColor, so it could not represent or generate examples using per-bar palettes.

Summary

This adds per-bar color palette support to the Bar playground style model and chart definition. The Bar settings now expose a Bar Colors palette sized to the current data point count. Style snapshot/code generation now include barColors, and colors are normalized to match series size for stable output. JS and JVM generator tests were extended to verify emitted barColors code and required Color imports.

Changes

• Add barColors to BarStyleState
• Add Bar Colors palette setting in BarChartDefinition
• Pass series count into bar style snapshot and normalize palette length
• Include barColors in generated style output
• Add codegen and compilation test coverage for barColors

Notes/Risk

• None

[github-actions]

✅ Playground Test Summary

• ✅ 33 tests completed successfully