feat(widgets): add reusable ChatBubble widget with role support

[SH20RAJ]

Summary

Adds a reusable widget to for chat UIs with role-based styling.

Changes

• add
• register module in
• document usage in

Roles

• = user (blue background, white text)
• = assistant (gray background, dark text)
• = system (yellow background, dark text)

Notes

• Build/test validation could not be run in this container because is unavailable in PATH.

[SH20RAJ]

Checked status: this PR is pending maintainer review/merge from upstream maintainers. I’m available to address feedback quickly.