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_source_service.py

@@ -267,6 +267,47 @@ async def test_start_recovery_arms_bypass_flag(db):
     assert "_backfill_bypass_seen" not in (co2 or {})
 
 
+@pytest.mark.asyncio
+async def test_start_recapture_arms_recapture_flag(db):
+    """#830: start_recapture arms the backfill state machine PLUS the
+    _backfill_recapture flag, surfaced on the record so the badge can label it
+    'Recapturing'. Mutually exclusive with recovery (clears bypass_seen); stop
+    clears it."""
+    from backend.app.services.source_service import BACKFILL_MAX_CHUNKS
+
+    artist = await _artist(db, "Alice")
+    svc = SourceService(db)
+    rec = await svc.create(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice",
+    )
+    # Pre-arm recovery, then recapture must clear bypass_seen (mutual exclusion).
+    await svc.start_recovery(rec.id)
+
+    updated = await svc.start_recapture(rec.id)
+    assert updated.backfill_state == "running"
+    assert updated.backfill_recapture is True
+    assert updated.backfill_bypass_seen is False
+    assert updated.backfill_runs_remaining == BACKFILL_MAX_CHUNKS
+
+    co = (await db.execute(
+        select(Source.config_overrides).where(Source.id == rec.id)
+    )).scalar_one()
+    assert co.get("_backfill_recapture") is True
+    assert "_backfill_bypass_seen" not in co
+
+    # to_dict carries the new field for the API/UI.
+    assert updated.to_dict()["backfill_recapture"] is True
+
+    # Stop clears the recapture flag too.
+    stopped = await svc.stop_backfill(rec.id)
+    assert stopped.backfill_recapture is False
+    co2 = (await db.execute(
+        select(Source.config_overrides).where(Source.id == rec.id)
+    )).scalar_one()
+    assert "_backfill_recapture" not in (co2 or {})
+
+
 @pytest.mark.asyncio
 async def test_start_backfill_raises_when_source_missing(db):
     svc = SourceService(db)