Refactor the AI/Chat Example 3 experience into a single reusable component
(src/components/AiAssistant.tsx): it renders the message bar inline and
portals its overlays (recent-chat popover + full-chat panel / modal) into a
positioned container, so the bar and the conversation can live in different
parts of the page.

- Chat.stories now consumes AiAssistant (single source of truth)
- Patterns/Compass → Example: the footer message bar is now the AiAssistant;
  its overlays float over the Compass content (recent popover above the
  footer, full chat in a corner), with a modal on narrow viewports
- bump @golden-passport/ds-patternfly to 0.4.0

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>