Build a form builder

• A palette of field types (text, number, email, textarea, select, checkbox, radio group) and an "Add" action (click or drag) that appends a field to the canvas
• Selecting a field on the canvas opens a config panel: label, name (unique and valid identifier), placeholder, required flag, options (for select and radio) and min or max rules
• Fields can be reordered (move up and down or drag) and removed
• The builder outputs a JSON schema (an array of field definitions, or JSON Schema) in a read-only panel that updates live, and can be copied
• A live preview renders the actual form from that JSON with validation (required, patterns, min and max) and shows errors on submit
• The builder state can be loaded from a JSON schema (import), and invalid JSON is reported without crashing

Only after every requirement works.

• Conditional fields shown when another field has a given value
• Sections and a multi-column layout
• Undo and redo of builder actions