Create visual diagrams from text descriptions using Mermaid syntax. Use when users request diagrams, flowcharts, charts, or visual representations of processes, architectures, relationships, timelines, or data. Supports flowcharts, sequence diagrams, class diagrams, state diagrams, ER diagrams, Gantt charts, git graphs, pie charts, timelines, mindmaps, user journeys, and more. Outputs markdown with mermaid code blocks.