Generated thumbnails on every card

Every design and component card in the catalog now shows a generated screenshot captured from the live demo, in place of a placeholder.

Sharper at every size

Thumbnails are captured by shrinking the capture viewport rather than cropping afterward, with a slight optical zoom applied so cards read clearly even at small sizes.

Improvements

• Added a dev-only screenshot generation API route and a GenerateScreenshotButton
• Captured component thumbnails at card width, without frame chrome
• Matched the mobile design card ratio to the captured screenshot