MockDataService.generateStringValue now returns a deterministic
https://picsum.photos URL when the field name matches one of:
imageUrl, image, photo, avatar, thumbnail, picture, cover, banner
(and *Url variants). Mirrors the @almadar/runtime change so server-mode
and runtime-mode produce visually consistent seed data instead of
faker.lorem.words() in image-bearing fields.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>