[hellopablo]

Summary

• User-cell profile images and the topbar avatar now use Nails\Cdn\Helper\Picture, with a 2x source at double the crop size (70px and 200px).
• Those are real CDN crop URLs, so a cached 1x file is never requested again with an @2x suffix.
• Permits the 70×70 crop the user cell needs. 200×200 was already permitted.
• Blank avatars stay a single image. Picture only accepts a CDN object.

Depends on nails/module-cdn#472. Without that change, a density-only source is emitted with an empty media attribute and the 2x crop loads on 1x displays too.

Test plan

• On a user list, confirm a profile image is a <picture> whose source is the 70px crop with media="(min-resolution: 2dppx)", and a user without a photo still shows the blank avatar.
• On a 2x display, confirm the network panel requests the 70px and 200px crops, not a cached filename with @2x appended.
• Confirm the topbar avatar still sits in the account cluster as a circle, including for an account with no profile image.