Put real photos on the trails people actually open (0 of 400 sampled have one)

Part of #1002.

Problem

0 of 400 trails sampled across production carry a photo of the trail; they carry Unsplash stock. The trail page labels this honestly — "Illustrative photo" — which is the right call and also an admission on every page. AllTrails leads with a real photo and a community gallery, and that single difference is most of what "they look higher quality" means.

Why this is tractable

We already attribute real imagery properly:

• app/Support/trailAreaPhotos.ts and app/Support/curatedTrailPhotos.ts source and credit Wikimedia Commons photos, with licence and source URL.
• The four Santa Barbara Island trails already show an attributed island photo, labelled as an area photo rather than passed off as the trail — tests/browser/trail-area-photos.test.ts pins that.
• Trail photo upload by athletes exists (TrailPhotoStoreAction), so community photos have somewhere to land.

The gap is coverage and aim, not capability.

Acceptance

• Photo sourcing pointed at the trails people actually open — most-viewed, most-saved, most-reviewed — rather than attempted across 596k rows.
• Area photos stay labelled as area photos; nothing implies a photo is of the trail when it is of the region.
• Licence, author and source URL carried for every sourced photo, as the existing helpers already do.
• A trail with no real photo keeps the illustrative label rather than gaining a misleading one.
• Coverage reported over the top-N set, so "did this work" has an answer.