Add 'concept' object to lesson schema with: - explanation: required string for 2-4 sentence concept explanation - diagram: optional string for SVG/ASCII art diagrams - containerVsItem: optional string for Flexbox-specific distinctions
Add 'concept' object to lesson schema with: - explanation: required string for 2-4 sentence concept explanation - diagram: optional string for SVG/ASCII art diagrams - containerVsItem: optional string for Flexbox-specific distinctions