[Feature] Message component (chat message layout: avatar + bubble + header/footer)

[djalmaaraujo]

Summary

Port the shadcn Message component to RubyUI. Message is the higher-level chat layout that wraps Bubble (see the Bubble component) inside an avatar + content + header/footer row. Built on top of the Bubble branch to reuse components.

Reference:

• Docs: https://ui.shadcn.com/docs/components/radix/message
• Source: apps/v4/registry/bases/radix/ui/message.tsx
• Styles: cn-message-* in apps/v4/registry/styles/style-rhea.css

Parts

• MessageGroup — stacks messages
• Message — row container, align: start|end (flips with avatar via flex-row-reverse)
• MessageAvatar — wraps the existing Avatar, anchors to bottom, lifts when a footer is present
• MessageContent — column holding bubbles; drives bubble alignment via group-data-[align=end]/message
• MessageHeader / MessageFooter — muted meta lines (name, timestamp, "Delivered")

Reuse (no new primitives)

• Avatar (existing) inside MessageAvatar
• Bubble / BubbleContent / BubbleGroup / BubbleReactions (Bubble branch) inside MessageContent

Alignment of bubbles is handled by Message — no changes to Bubble needed.

Out of scope

• Marker (the "is typing…" indicator) is a separate shadcn component; not ported here. Demo will use plain text instead.

Tasks

• gem/lib/ruby_ui/message/* (6 parts) + translate cn-message-* to Tailwind v4
• gem/test/ruby_ui/message_test.rb
• gem/lib/generators/ruby_ui/dependencies.yml → message depends on Avatar, Bubble
• Docs view + route + controller + menu + site_files