feat(translation): re-translate on model change — artist-scoped + global re-run (#146)

retranslate_posts resets the 5 translation columns to NULL for a scoped set of posts (all, or WHERE artist_id IN ids) then reuses the untranslated sweep to re-run them, chasing the tail until drained (run-until-done). Interpreter cache keys on engine_version so a changed model re-translates, an unchanged one is cache-fast. Reset only happens when the service is configured+healthy so translations are never wiped when they can't be rebuilt. New POST /settings/translation/retranslate (artist_id | all=true). UI: per-artist 'Re-translate posts' on the Artist Management tab + 'Re-translate all' in the Settings Translation card, both with confirm dialogs. No migration (reuses m143 columns).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/settings/TranslationCard.vue

@@ -47,16 +47,49 @@
         prepend-icon="mdi-translate" :loading="running"
         :disabled="!enabled || !baseUrl" @click="onRun"
       >Translate now</v-btn>
+      <v-btn
+        size="small" variant="tonal" rounded="pill"
+        prepend-icon="mdi-refresh" :loading="retranslating"
+        :disabled="!enabled || !baseUrl" @click="confirmAll = true"
+      >Re-translate all</v-btn>
       <span v-if="status" class="fc-muted text-caption">
         {{ status.untranslated_count }}
         post{{ status.untranslated_count === 1 ? '' : 's' }} awaiting translation
       </span>
     </div>
+    <p class="fc-muted text-caption mt-2 mb-0">
+      Use <strong>Re-translate all</strong> after switching the Interpreter model —
+      it clears every stored translation and re-runs it through the new model
+      (unchanged text is served from cache, so it's cheap). To refresh just one
+      artist, use the Re-translate button on that artist's page.
+    </p>
 
     <v-alert
       v-if="err" type="error" variant="tonal" density="compact"
       class="mt-3" closable @click:close="err = null"
     >{{ err }}</v-alert>
+
+    <!-- m146: re-translate-everything is a bigger hammer than 'Translate now'
+         (it clears + rebuilds all translations), so it asks first. -->
+    <v-dialog v-model="confirmAll" max-width="440">
+      <v-card>
+        <v-card-title>Re-translate everything?</v-card-title>
+        <v-card-text class="text-body-2">
+          This clears the stored translation for <strong>every</strong> post and
+          re-runs them through your current Interpreter model. Text that hasn't
+          changed comes back from the cache instantly; anything the new model
+          translates differently is refreshed. It runs in the background until
+          done.
+        </v-card-text>
+        <v-card-actions>
+          <v-spacer />
+          <v-btn variant="text" @click="confirmAll = false">Cancel</v-btn>
+          <v-btn
+            color="accent" :loading="retranslating" @click="onRetranslateAll"
+          >Re-translate all</v-btn>
+        </v-card-actions>
+      </v-card>
+    </v-dialog>
   </MaintenanceTile>
 </template>
 
@@ -75,6 +108,8 @@ const baseUrl = ref('')
 const targetLang = ref('en')
 const busy = ref(false)
 const running = ref(false)
+const retranslating = ref(false)
+const confirmAll = ref(false)
 const testing = ref(false)
 const testResult = ref(null)   // null = not tested this session; true/false = last result
 const status = ref(null)
@@ -159,4 +194,18 @@ async function onRun() {
     setTimeout(loadStatus, 1500)   // let the sweep make a dent, then refresh
   }
 }
+async function onRetranslateAll() {
+  retranslating.value = true
+  err.value = null
+  try {
+    await api.post('/api/settings/translation/retranslate', { body: { all: true } })
+    confirmAll.value = false
+    toast({ text: 'Re-translating all posts…', type: 'success' })
+  } catch (e) {
+    err.value = e.message
+  } finally {
+    retranslating.value = false
+    setTimeout(loadStatus, 1500)   // reset spikes the untranslated count — refresh it
+  }
+}
 </script>