Fix card image priority: own > mined from article > inherited

The resolved (inheriting) Node.image was checked before mining the
article, so a front-page banner image shadowed the articles' own
extracted figures everywhere: card covers, og:image and the editor's
card previews.

frontend/src/BannerEditor.vue

@@ -74,7 +74,8 @@ const image = ref('')
 const imageResolved = ref('')
 const imageSource = ref('')
 // The image the server would mine from the article itself — the card
-// previews fall back to it when no node image resolves (mirrors og:image).
+// previews fall back to it when the node has no image of its own, and it
+// beats an inherited one (mirrors og:image).
 const imageMined = ref('')
 // Whether the page has children (from the doc message): an own share
 // image is inherited by the whole section.
@@ -86,22 +87,25 @@ const imageLabel = computed(() => {
       ? `card image: set for this article — used in /${path.value}/*`
       : 'card image: set for this article'
   }
+  if (imageMined.value) return 'card image: from the article'
   if (imageResolved.value) {
     const where = imageSource.value === '' ? 'the front page' : `/${imageSource.value}`
     return `card image: inherited from ${where}`
   }
-  if (imageMined.value) return 'card image: from the article'
   return 'card image: none'
 })
 // The page title and description (from the doc message) feed the mock card
 // previews; empty shows placeholder bars / text instead.
 const pageTitle = ref('')
 const pageDesc = ref('')
-// The image the Twitter cards preview with: the resolved node card image,
-// else the mined article image (what og:image would use). image_resolved is
-// a bare store hash; image_mined is already a src path.
+// The image the Twitter cards preview with: the node's own card image,
+// else the mined article image, else the inherited node image (what
+// og:image would use). image/image_resolved are bare store hashes;
+// image_mined is already a src path.
 const cardImage = computed(() =>
-  imageResolved.value ? `/_f/${imageResolved.value}` : imageMined.value,
+  image.value
+    ? `/_f/${image.value}`
+    : imageMined.value || (imageResolved.value ? `/_f/${imageResolved.value}` : ''),
 )
 // Card-mode override (Node.large, per-article, NOT inherited):
 // null = automatic, false = small, true = large.