feat(ui): translation-forward post text + Settings card (#143 step 5)

PostCard + modal ProvenancePanel show the English title/description by default when
a translation exists, with a per-card "show original (<lang>)" toggle — translated
bodies render as plain text, originals keep their sanitized HTML. New
TranslationCard in Settings → Ingestion & filters: enable switch, Interpreter base
URL (generic placeholder, no default host), target language, a reachability
indicator + untranslated-posts count + "Translate now".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

frontend/src/components/modal/ProvenancePanel.vue

@@ -42,13 +42,23 @@
             · {{ e.post.attachment_count }} files
           </span>
         </div>
+        <div v-if="hasTranslation(e)" class="fc-prov__actions">
+          <a
+            href="#" @click.prevent="toggleOrig(e.provenance_id)"
+          >{{ showOrig[e.provenance_id] ? 'Show translation' : `Show original${langLabel(e)}` }}</a>
+        </div>
         <div v-if="e.post.description_html" class="fc-prov__actions">
           <a
             href="#" @click.prevent="toggleDesc(e.provenance_id)"
           >{{ expanded[e.provenance_id] ? 'Hide description ▴' : 'Show description ▾' }}</a>
         </div>
+        <!-- Translated body = plain text; original = sanitized HTML (#143). -->
+        <p
+          v-if="showTranslated(e) && expanded[e.provenance_id] && e.post.description_translated"
+          class="fc-prov__desc"
+        >{{ e.post.description_translated }}</p>
         <div
-          v-if="e.post.description_html && expanded[e.provenance_id]"
+          v-else-if="e.post.description_html && expanded[e.provenance_id]"
           class="fc-prov__desc" v-html="e.post.description_html"
         />
       </article>
@@ -117,8 +127,12 @@ const effectiveImage = computed(() => props.image ?? modal.current)
 // 2026-05-28. Reset when the viewed image changes.
 const expanded = reactive({})
 function toggleDesc(id) { expanded[id] = !expanded[id] }
+// Per-entry "show the original (untranslated) text" toggle (#143).
+const showOrig = reactive({})
+function toggleOrig(id) { showOrig[id] = !showOrig[id] }
 watch(() => effectiveId.value, () => {
   for (const k of Object.keys(expanded)) delete expanded[k]
+  for (const k of Object.keys(showOrig)) delete showOrig[k]
 })
 
 watch(
@@ -157,10 +171,23 @@ const show = computed(() => {
 const attachments = computed(() => state.value?.attachments || [])
 
 function postDate(e) { return formatPostDate(e.post.date) }
+// Translation-forward (#143): show the English by default when present.
+function hasTranslation(e) {
+  return !!(e.post.title_translated || e.post.description_translated)
+}
+function showTranslated(e) {
+  return hasTranslation(e) && !showOrig[e.provenance_id]
+}
+function langLabel(e) {
+  return e.post.translated_source_lang ? ` (${e.post.translated_source_lang})` : ''
+}
 function postTitle(e) {
   // Titles can arrive as stored HTML (e.g. "<strong>…</strong>"); render
   // as plain text (the CSS makes it bold).
-  return toPlainText(e.post.title) || `Post ${e.post.external_post_id}`
+  const t = showTranslated(e) && e.post.title_translated
+    ? e.post.title_translated
+    : e.post.title
+  return toPlainText(t) || `Post ${e.post.external_post_id}`
 }
 
 function openPost(postId, artistId) {