fix: a one-message Discord drop is labelled a Discord message, not a grouping (4390)

It stays synthetic, since teaser matching looks only at drops, but the card
no longer claims "Grouped from 1 Discord message" / "grouped by
FabledCurator" over a single message. The marker chip stays and reads
"from Discord".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

frontend/src/components/posts/PostCard.vue

@@ -20,7 +20,7 @@
         class="fc-post-card__synthetic" :title="synthesisTitle"
       >
         <v-icon icon="mdi-auto-fix" size="x-small" start />
-        grouped by FabledCurator
+        {{ synthesisChip }}
       </v-chip>
       <RouterLink
         :to="{ name: 'artist', params: { slug: post.artist.slug } }"
@@ -270,11 +270,18 @@ const plainTitle = computed(() => toPlainText(props.post.post_title))
 // post dict by hand, must degrade to "not synthetic" rather than throw.
 const synthesized = computed(() => Boolean(props.post.synthesized_by))
 const messageCount = computed(() => props.post.synthesis?.message_count ?? 0)
+// A drop of one message stays a synthetic post (teaser matching only looks at
+// drops), but there is nothing grouped in it — #4390: "Grouped from 1 Discord
+// message" described a wrapper, not a grouping. Say what it is instead.
 const synthesisTitle = computed(() => {
   const n = messageCount.value
   if (!n) return 'Grouped from Discord'
-  return `Grouped from ${n} Discord message${n === 1 ? '' : 's'}`
+  if (n === 1) return 'Discord message'
+  return `Grouped from ${n} Discord messages`
 })
+const synthesisChip = computed(() =>
+  messageCount.value === 1 ? 'from Discord' : 'grouped by FabledCurator'
+)
 
 const hero = computed(() => images.value[0])