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, 25 insertions, 1 deletions

diff --git a/app/views/assets/show.html.erb b/app/views/assets/show.html.erb
index ff00883c..a0e4e464 100644
--- a/app/views/assets/show.html.erb
+++ b/app/views/assets/show.html.erb
@@ -17,7 +17,10 @@
     </div>
 
     <div class="node_description">Thumbnail</div>
-    <div class="node_content"><%= image_tag @asset.upload.url(:medium), style: "max-width: 300px; max-height: 300px;" %></div>
+    <% if @asset.has_variant?(:medium) %>
+      <div class="node_description">Thumbnail</div>
+      <div class="node_content"><%= image_tag @asset.upload.url(:medium), style: "max-width: 300px; max-height: 300px;" %></div>
+    <% end %>
 
     <div class="node_description">Public Path</div>
     <div class="node_content">
@@ -30,6 +33,27 @@
       </button>
     </div>
 
+    <div class="node_description">Creator</div>
+    <div class="node_content"><%= @asset.creator.presence || "—" %></div>
+
+    <div class="node_description">Source</div>
+    <div class="node_content">
+      <% if @asset.source_url.present? %>
+        <%= link_to @asset.source_url, @asset.source_url %>
+      <% else %>
+        —
+      <% end %>
+    </div>
+
+    <div class="node_description">License</div>
+    <div class="node_content">
+      <% if (license = AssetLicense.find(@asset.license_key)) %>
+        <%= t("asset_licenses.#{license.key}") %>
+      <% else %>
+        —
+      <% end %>
+    </div>
+
     <div class="node_description">Content Type</div>
     <div class="node_content"><%= @asset.upload.content_type %></div>