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.

2 files changed, 12 insertions, 2 deletions

diff --git a/app/controllers/assets_controller.rb b/app/controllers/assets_controller.rb
index d150e06..becfe13 100644
--- a/app/controllers/assets_controller.rb
+++ b/app/controllers/assets_controller.rb
@@ -89,6 +89,6 @@ class AssetsController < ApplicationController
   private
 
     def asset_params
-      params.require(:asset).permit(:name, :upload)
+      params.require(:asset).permit(:name, :upload, :creator, :source_url, :license_key)
     end
 end
diff --git a/app/controllers/related_assets_controller.rb b/app/controllers/related_assets_controller.rb
index 5af73fc..da82cde 100644
--- a/app/controllers/related_assets_controller.rb
+++ b/app/controllers/related_assets_controller.rb
@@ -39,7 +39,17 @@ class RelatedAssetsController < ApplicationController
   end
 
   def update
-    @node.editable_page.related_assets.find(params[:id]).insert_at(params[:position].to_i)
+    related = @node.editable_page.related_assets.find(params[:id])
+
+    if params.key?(:headline)
+      RelatedAsset.transaction do
+        @node.editable_page.related_assets.update_all(headline: false)
+        related.update!(headline: true) if params[:headline] == "true"
+      end
+    else
+      related.insert_at(params[:position].to_i)
+    end
+
     head :ok
   end