Instance AI timeline components consolidated and styled

The Instance AI chat interface in the editor is getting a visual and architectural refresh. Several timeline components—AgentNodeSection, BuilderCard, ResearchCard, DataTableCard, and ExecutionPreviewCard—were doing overlapping work with their own styling and markup. These have been consolidated into three new reusable components: TimelineStepButton for collapsible triggers, DataSection for structured content blocks, and ButtonLike for inline status indicators.

The chat background is now lighter (--color--background--light-2), message text is larger, and input styling matches the main Chat hub more closely. Icon colors are being standardized with explicit color props (color="primary", color="success") instead of relying on implicit defaults.

Error states are now handled by the N8nCallout component rather than custom-styled divs, bringing consistency with the design system's established patterns. The auto-focus behavior for the chat input has been improved—it now triggers on mount and whenever the input ref rebinds after messages load.

These changes sit in the @n8n/editor-ui's AI feature module, affecting how users interact with agent activity timelines, tool call results, and delegation cards.