Make headline images explicit, add asset credits

- related_assets gains a `headline` boolean (DB-enforced: at most one
  per page), replacing "first image by position" as the headline
  rule. A rake task backfills the current first image on every live
  head/draft, so nothing changes visually until an editor changes it.
- The image picker sidebar gets a star toggle reflecting the flag;
  the TinyMCE inline-image picker's badge now reads it too, instead
  of assuming position 0.
- No headline chosen (or none attached) now falls back to the
  gallery-count caption itself becoming the lightbox trigger, instead
  of the gallery being unreachable.
- Assets gain creator, source_url, and license_key (against a new
  config/asset_licenses.yml dictionary). asset_credit renders a
  degrading attribution line, reused as a hidden per-image glightbox
  caption so credit is one click away for every image, not only the
  headline's always-visible one.
- Fixed: asset thumbnails rendered unconditionally regardless of
  whether a real variant exists on disk. Asset#has_variant? checks
  file existence, not content type -- some legacy PDFs have real
  pre-rewrite thumbnails a content-type check would have hidden.
- assets#new/edit rebuilt onto the same node_description/node_content
  layout as assets#show, picking up the three new fields in the
  process.

1 files changed, 20 insertions, 0 deletions

diff --git a/lib/tasks/assets.rake b/lib/tasks/assets.rake
index 563dfad..9d4b048 100644
--- a/lib/tasks/assets.rake
+++ b/lib/tasks/assets.rake
@@ -16,4 +16,24 @@ namespace :assets do
       puts "Regenerated variants for Asset##{asset.id} (#{asset.name})"
     end
   end
+
+desc "One-shot: flag each live page's current first-by-position image as its headline"
+  task backfill_headline: :environment do
+    count = 0
+    page_ids = (Node.where.not(head_id: nil).pluck(:head_id) +
+                Node.where.not(draft_id: nil).pluck(:draft_id)).uniq
+
+    Page.where(id: page_ids).find_each do |page|
+      next if page.related_assets.where(headline: true).exists?
+
+      first_image = page.related_assets.joins(:asset).merge(Asset.images).order(:position).first
+      next unless first_image
+
+      first_image.update!(headline: true)
+      count += 1
+    end
+
+    puts "Flagged #{count} pages' current first image as headline."
+  end
+
 end