Collection-level branding and a featured-collections display for the demo tenants

[ShanaLMoore]

Summary

Carried forward from #32, which is closed as superseded by Session 2. Session 2 delivered the corpus (112 works, four tenants, validation green), but two of #32's acceptance criteria were not part of it and are not owned by any session prompt.

Collections in the corpus have titles, descriptions, and members, but no visual identity, and the homepage features individual works rather than collections. Both matter for the browse-and-evaluate experience the initiative is measured on, since collection browsing is one of the evaluator questions #32 recorded.

Acceptance Criteria

• Every corpus collection has a cover image and a banner, sourced from the existing licensed corpus media so no new provenance work is needed
• Collection branding is captured in hyku-demo-seed so it survives a tenant rebuild rather than being hand-applied
• The tenant homepage offers a featured-collections display, tiled, in addition to featured works
• The validation suite asserts collection branding is present, in the same style as the existing featured-works assertions

Notes

• Featured works already exist and are validated: scripts/feature_works.rb, restored on reset by DemoTenantResetService. This ticket is about collections, which have no equivalent.
• Related but not the same: Branding assets in the seed repo: capture and re-upload logos/banners/favicons via the apply task (Session 10, pulled forward) #132 covers capturing tenant-level branding assets (logos, banners, favicons) via the apply task. Collection-level branding is a separate surface and should probably reuse whatever mechanism Branding assets in the seed repo: capture and re-upload logos/banners/favicons via the apply task (Session 10, pulled forward) #132 lands.
• If the featured-collections display needs product code rather than configuration, it belongs upstream in samvera/hyku as a themeable component, consistent with how the Session 4b themes shipped.
• Source: Create good data in demo tenant (collection + works) #32 acceptance criteria, "Collections have a cover image, banner" and "Collections are featured on the homepage".