Render PDF headlines as document cards, not lightbox images

A starred PDF previously ran through the same crop-and-lightbox path
a photo does -- exactly the awkward treatment explicit headline
designation was meant to avoid. _headline_image.html.erb now branches
on @headline_asset.pdf?: a PDF renders as a linked card (a :medium
thumbnail, a file icon, its name), no gallery participation at all.
The existing image-headline and gallery-fallback logic is otherwise
unchanged, now scoped to an image-specific headline only.

Other attached PDFs -- headlined or not -- list below as plain links,
same reasoning as why non-headline photos still get a gallery
trigger: an attached document shouldn't go invisible just because
nothing's been starred yet.

headline_image's own render guard needed widening to cover a page
with PDFs attached but no images and no headline at all -- the one
case none of the existing conditions accounted for.

1 files changed, 2 insertions, 0 deletions

diff --git a/app/models/asset.rb b/app/models/asset.rb
index 9feefa9..ba9c2f0 100644
--- a/app/models/asset.rb
+++ b/app/models/asset.rb
@@ -10,6 +10,8 @@ class Asset < ApplicationRecord
   scope :images,    -> { where(:upload_content_type => IMAGE_CONTENT_TYPES) }
   scope :documents, -> { where(:upload_content_type => ["application/pdf", "text/plain", "text/rtf"]) }
   scope :audio,     -> { where(:upload_content_type => ["audio/mpeg", "audio/x-m4a", "audio/wav", "audio/x-wav"]) }
+  scope :pdfs,      -> { where(:upload_content_type => PDF_CONTENT_TYPE) }
+
   scope :headline_eligible, -> { where(:upload_content_type => IMAGE_CONTENT_TYPES + [PDF_CONTENT_TYPE]) }
 
   validates :license_key, inclusion: { in: -> { AssetLicense.keys } }, allow_blank: true