AI builder wizard UI polished with smarter scrolling and popovers

The AI builder setup wizard had several rough edges that made it feel unresponsive. When switching between cards of different heights, the chat wouldn't scroll to keep the wizard footer in view. Popover dropdowns would clip against overflow boundaries instead of flipping to a visible position. And the messages container always added bottom padding, even when the rating overlay wasn't present.

The wizard now auto-scrolls when navigating between cards of different heights. The scroll trigger uses requestAnimationFrame to ensure the new card has been laid out before reading scrollHeight. A Vue provide/inject pattern wires the chat component's scrollToBottom method to the wizard without tight coupling.

Popovers gained a collisionPadding prop defaulting to 5px. Dropdowns now flip upward before clipping against overflow boundaries. The messages container only applies extra bottom padding when the rating overlay is shown.

The fixes span the design system's chat and popover components, plus the editor UI's wizard and agent components. The provide/inject refactor makes the chat-to-wizard relationship cleaner and more maintainable going forward.