refactor(ingest): per-post handling into run stdout via a downloader outcome (#842)

Two corrections from operator review:
1. Reuse the existing 'Raw stdout' panel instead of a bespoke structured UI
   section — the native ingester now writes a per-post line into the run stdout
   (parity with gallery-dl's per-file stdout), so the per-post handling shows in
   the panel the operator already uses.
2. DRY: stop re-reading post['attributes'] inline in ingest_core. write_post_record
   now returns a PostRecordOutcome (path, post_type, title, body_chars) — mirroring
   the download_post -> MediaOutcome contract — and the downloader owns the read;
   ingest_core only formats the outcome into the log line.

Reverts the post_diagnostics metadata field + DownloadDetailModal 'Post capture'
section added earlier. Per-post line: 'post <id> [<post_type>] body: N chars' (+
' — EMPTY' when 0), so an empty body is self-explanatory by post_type.

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

tests/test_download_service.py

@@ -60,11 +60,10 @@ def _make_fake_dl_result(
     *, success=True, written_paths=None, quarantined_paths=None,
     files_downloaded=0, error_type=None, error_message=None,
     stdout="", stderr="", cursor=None, run_stats=None, posts_processed=0,
-    relink_source_paths=None, post_diagnostics=None,
+    relink_source_paths=None,
 ):
     return SimpleNamespace(
         relink_source_paths=relink_source_paths or [],
-        post_diagnostics=post_diagnostics or [],
         success=success,
         url="https://patreon.com/alice",
         artist_slug="alice",
@@ -821,28 +820,6 @@ async def test_recapture_mode_selected_and_flag_cleared_on_complete(
     assert "_backfill_recapture" not in co
 
 
-@pytest.mark.asyncio
-async def test_post_diagnostics_written_to_event_metadata(
-    db, db_sync, tmp_path, seed_artist_and_source,
-):
-    """#842: per-post body diagnostics land on the DownloadEvent.metadata_ so the
-    UI can show how each post was handled (post_type + body length)."""
-    _artist, source = seed_artist_and_source
-    diag = [
-        {"post_id": "p1", "title": "Has body", "post_type": "image_file", "body_chars": 42},
-        {"post_id": "p2", "title": "Empty poll", "post_type": "poll", "body_chars": 0},
-    ]
-    svc, _ = _backfill_svc(db, db_sync, tmp_path, _make_fake_dl_result(
-        success=True, post_diagnostics=diag,
-    ))
-    await svc.download_source(source.id)
-
-    ev = (await db.execute(
-        select(DownloadEvent).order_by(DownloadEvent.id.desc()).limit(1)
-    )).scalar_one()
-    assert ev.metadata_["post_diagnostics"] == diag
-
-
 @pytest.mark.asyncio
 async def test_partial_error_type_maps_to_ok_status(
     db, db_sync, tmp_path, seed_artist_and_source,