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, 31 insertions, 0 deletions

diff --git a/test/models/asset_license_test.rb b/test/models/asset_license_test.rb
new file mode 100644
index 00000000..9f2d04f8
--- /dev/null
+++ b/test/models/asset_license_test.rb
@@ -0,0 +1,31 @@
+require 'test_helper'
+
+class AssetLicenseTest < ActiveSupport::TestCase
+  test "find returns a populated entry for a known key" do
+    entry = AssetLicense.find("cc_by_4")
+
+    assert_equal "cc_by_4", entry.key
+    assert_equal "https://creativecommons.org/licenses/by/4.0/", entry.url
+    assert entry.requires_attribution
+    assert_equal "license", entry.style
+  end
+
+  test "find returns nil for an unknown or blank key" do
+    assert_nil AssetLicense.find("not_a_real_license")
+    assert_nil AssetLicense.find(nil)
+    assert_nil AssetLicense.find("")
+  end
+
+  test "keys includes every dictionary entry" do
+    assert_includes AssetLicense.keys, "cc0"
+    assert_includes AssetLicense.keys, "own_work"
+  end
+
+  test "a note-style entry has no attribution requirement and no url" do
+    entry = AssetLicense.find("own_work")
+
+    assert_not entry.requires_attribution
+    assert_nil entry.url
+    assert_equal "note", entry.style
+  end
+end