fix: a download is marked seen only after it is imported

A run killed between download and import left its files on disk and in the
seen-ledger but never in the library, and every later walk trusted the
ledger. TamadaHeijun's 12PCG post lost 7 of 13 images this way (stranded
run 90402), which read as the duplicates filter.

The ingester now hands phase 3 a mark_seen_after_import hook, called after
the import loop. A file on disk with no ImageRecord at its path is fed to
import, not reconciled into the ledger. Recapture reaches files already
orphaned, because it looks past the ledger to the disk.

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

frontend/src/components/subscriptions/SourceActions.vue

@@ -45,8 +45,9 @@
       >
         <v-list-item-title>Recapture post text &amp; links</v-list-item-title>
         <v-list-item-subtitle>
-          Re-grab every post's body + external links and localize inline images
-          already on disk — without re-downloading media
+          Re-grab every post's body + external links, localize inline images
+          already on disk, and import any downloaded file that never reached the
+          library — without re-downloading media
         </v-list-item-subtitle>
       </v-list-item>
       <v-divider v-if="isNative && !running" />