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, 15 insertions, 0 deletions

diff --git a/app/models/asset_license.rb b/app/models/asset_license.rb
new file mode 100644
index 00000000..ca66d40a
--- /dev/null
+++ b/app/models/asset_license.rb
@@ -0,0 +1,15 @@
+class AssetLicense
+  Entry = Struct.new(:key, :url, :requires_attribution, :style, keyword_init: true)
+
+  DICTIONARY = YAML.load_file(Rails.root.join("config", "asset_licenses.yml")).freeze
+
+  def self.keys
+    DICTIONARY.keys
+  end
+
+  def self.find(key)
+    entry = DICTIONARY[key.to_s] if key.present?
+    return nil unless entry
+    Entry.new(key: key.to_s, url: entry["url"], requires_attribution: entry["requires_attribution"], style: entry["style"])
+  end
+end