feat(ingest): Recapture mode — re-grab post bodies/links + localize on-disk inline images (#830)

A plain backfill gates post-body capture on the seen-ledger, so a post whose
media is already on disk AND whose post key is already seen never gets its body
recaptured (operator-flagged: Industrial Lust description missing). Recovery
recaptures unconditionally but re-downloads the whole source.

New 'recapture' walk mode (4th beside tick/backfill/recovery): bypasses the
post-record gate so EVERY post's body + external links are re-captured
(detail-fetching empty bodies) WITHOUT re-downloading on-disk media; and
surfaces already-present media via a separate non-deleting relink channel so the
importer backfills ImageRecord.source_filehash for inline-image localization.

- ingest_core: recapture mode + recapture_records gate bypass + relink collect
- patreon_downloader: recapture surfaces seen-on-disk as skipped_disk(path),
  never refetches seen-missing media, still downloads genuinely-new
- importer.relink_source_filehash: NULL-only sha256 backfill, never unlinks
- download_service: mode derivation + phase-3 relink loop + lifecycle clear
- source_service/api: start_recapture + backfill_recapture field + action
- frontend: Recapture kebab action + 'Recapturing' badge across SourceActions/
  Row/Card/SubscriptionsTab + sources store
- tests across ingester/downloader/importer/source_service/api/download_service

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/subscriptions/SubscriptionsTab.vue

@@ -138,7 +138,7 @@
               :source="item.singleSource"
               :checking="store.checkingIds.has(item.singleSource.id)"
               @check="onCheck" @backfill="onBackfill"
-              @recover="onRecover" @remove="removeSource"
+              @recover="onRecover" @recapture="onRecapture" @remove="removeSource"
             />
             <v-btn icon size="small" variant="text" @click.stop="openEditSource(item.singleSource)">
               <v-icon>mdi-pencil</v-icon>
@@ -214,6 +214,7 @@
                     @check="onCheck"
                     @backfill="onBackfill"
                     @recover="onRecover"
+                    @recapture="onRecapture"
                   />
                   <tr v-if="item.sources.length === 0">
                     <td colspan="8" class="fc-subs__sources-empty">
@@ -291,6 +292,7 @@
             @check="onCheck"
             @backfill="onBackfill"
             @recover="onRecover"
+            @recapture="onRecapture"
           />
           <div v-if="item.sources.length === 0" class="fc-subs__sources-empty">
             No sources yet. Tap + to add one.
@@ -646,6 +648,22 @@ async function onRecover(source) {
   }
 }
 
+// #830: arm a recapture walk (Patreon-only) — re-grab every post's body +
+// external links and localize on-disk inline images, without re-downloading
+// media. Reuses the backfill lifecycle/badge; stop via the same Stop control.
+async function onRecapture(source) {
+  try {
+    await store.recaptureSource(source.id, source.artist_id)
+    toast({ text: `Recapture started for ${source.artist_name}`, type: 'success' })
+    // recaptureSource patches the source in place — no full reload.
+  } catch (e) {
+    toast({
+      text: `Recapture start failed: ${e?.body?.detail || e?.message || e}`,
+      type: 'error',
+    })
+  }
+}
+
 async function checkAll(group) {
   let ok = 0
   let conflict = 0