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>

tests/test_patreon_downloader.py

@@ -206,6 +206,54 @@ def test_skip_disk(tmp_path):
     assert existing.read_bytes() == b"already here"  # untouched
 
 
+def test_recapture_surfaces_seen_on_disk_without_download(tmp_path):
+    """#830 recapture: a seen item that IS on disk is surfaced as skipped_disk
+    (with its path, for source_filehash backfill) — NOT tier-1 short-circuited,
+    and never re-downloaded."""
+    session = _FakeSession()
+    dl = _downloader(tmp_path, session=session)
+    post_dir = tmp_path / "artist-x" / "patreon" / "2026-05-01_1001_My Post Title"
+    post_dir.mkdir(parents=True)
+    existing = post_dir / "01_media1.png"
+    existing.write_bytes(b"already here")
+
+    outcomes = dl.download_post(
+        _post(), [_img("media1.png")], "artist-x",
+        is_seen=lambda m: True, recapture=True,
+    )
+    assert outcomes[0].status == "skipped_disk"
+    assert outcomes[0].path == existing
+    assert session.calls == []                        # no re-download
+    assert existing.read_bytes() == b"already here"    # untouched
+
+
+def test_recapture_does_not_refetch_seen_missing(tmp_path):
+    """#830 recapture: a seen item that's NOT on disk is left alone (skipped_seen,
+    no download) — refetching is recovery's job, not recapture's."""
+    session = _FakeSession()
+    dl = _downloader(tmp_path, session=session)
+    outcomes = dl.download_post(
+        _post(), [_img("media1.png")], "artist-x",
+        is_seen=lambda m: True, recapture=True,
+    )
+    assert outcomes[0].status == "skipped_seen"
+    assert outcomes[0].path is None
+    assert session.calls == []                        # not refetched
+
+
+def test_recapture_still_downloads_genuinely_new(tmp_path):
+    """#830 recapture: media that is neither seen nor on disk still downloads — a
+    recapture walk is thorough, it just doesn't re-pull existing files."""
+    session = _FakeSession()
+    dl = _downloader(tmp_path, session=session)
+    outcomes = dl.download_post(
+        _post(), [_img("media1.png")], "artist-x",
+        is_seen=lambda m: False, recapture=True,
+    )
+    assert outcomes[0].status == "downloaded"
+    assert outcomes[0].path is not None
+
+
 def test_video_routes_to_ytdlp(tmp_path, monkeypatch):
     session = _FakeSession()
     dl = _downloader(tmp_path, session=session)