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>

backend/app/services/patreon_downloader.py

@@ -198,6 +198,7 @@ class PatreonDownloader:
         *,
         is_seen: Callable[[object], bool] = lambda m: False,
         should_stop: Callable[[], bool] = lambda: False,
+        recapture: bool = False,
     ) -> list[MediaOutcome]:
         """Download every media item of one post; return per-item outcomes.
 
@@ -212,6 +213,11 @@ class PatreonDownloader:
         re-checks the budget between posts), so we honour the deadline mid-post
         and return the items done so far — the rest re-fetch next chunk (they
         were never marked seen). Bounds chunk overrun to one media download.
+
+        `recapture` (#830): don't re-download already-present media, but DO surface
+        on-disk media as `skipped_disk` (with its path) even when the seen-ledger
+        would tier-1 skip it — so the engine can backfill source_filehash for
+        inline-image localization. Genuinely-missing seen media is NOT refetched.
         """
         post_dir = self.images_root / artist_slug / "patreon" / _post_dir_name(post)
         outcomes: list[MediaOutcome] = []
@@ -221,7 +227,10 @@ class PatreonDownloader:
                 break
             try:
                 outcomes.append(
-                    self._download_one(post, media, post_dir, artist_slug, i, is_seen)
+                    self._download_one(
+                        post, media, post_dir, artist_slug, i, is_seen,
+                        recapture=recapture,
+                    )
                 )
             except Exception as exc:  # resilient: isolate one item's failure
                 log.warning(
@@ -243,9 +252,15 @@ class PatreonDownloader:
         artist_slug: str,
         index: int,
         is_seen: Callable[[object], bool],
+        *,
+        recapture: bool = False,
     ) -> MediaOutcome:
-        # tier-1: seen ledger (injected; no DB here).
-        if is_seen(media):
+        # tier-1: seen ledger (injected; no DB here). In recapture mode we DON'T
+        # short-circuit here — we fall through to the disk check so an on-disk
+        # seen file is surfaced as skipped_disk (with its path) for source_filehash
+        # backfill; a seen file that's NOT on disk is left alone (not refetched).
+        seen = is_seen(media)
+        if seen and not recapture:
             return MediaOutcome(media=media, status="skipped_seen", path=None, error=None)
 
         nn = f"{index:02d}"
@@ -265,6 +280,12 @@ class PatreonDownloader:
                     media=media, status="skipped_disk", path=existing, error=None
                 )
 
+        # recapture: a seen item that isn't on disk is NOT re-downloaded (that's
+        # recovery's job) — recapture only re-grabs post text + localizes existing
+        # files. Returns skipped_seen so the run-of-seen / counts stay consistent.
+        if seen:
+            return MediaOutcome(media=media, status="skipped_seen", path=None, error=None)
+
         post_dir.mkdir(parents=True, exist_ok=True)
 
         # Pace real downloads only (the skips above already returned). plan #703.