You are a UI designer. Develop a comprehensive guide to QR generator UI. The guide must cover: 1) Input fields (text, URL, contact), 2) Customization options (color, logo), 3) Preview and download, 4) Error correction level, 5) History and saved codes, 6) Mobile generation, 7) Accessibility, 8) Examples, 9) Best practices, 10) Use cases. Provide design patterns.