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_patreon_downloader.py

@@ -18,6 +18,7 @@ from backend.app.services.patreon_client import MediaItem
 from backend.app.services.patreon_downloader import (
     MediaOutcome,
     PatreonDownloader,
+    PostRecordOutcome,
     _sanitize,
 )
 from backend.app.utils.sidecar import find_sidecar
@@ -646,14 +647,17 @@ def test_write_post_record_writes_enriched_post_only_sidecar(tmp_path):
     )
     post = _post()
     post["attributes"]["content"] = ""  # media-less post, empty feed body
-    sc = dl.write_post_record(post, "artist-x")
+    rec = dl.write_post_record(post, "artist-x")
 
-    assert sc is not None
-    assert sc.name == "_post.json"  # can't collide with a media `NN_*.json`
-    data = json.loads(sc.read_text())
+    assert isinstance(rec, PostRecordOutcome)
+    assert rec.path is not None
+    assert rec.path.name == "_post.json"  # can't collide with a media `NN_*.json`
+    data = json.loads(rec.path.read_text())
     assert data["id"] == "1001"
     assert data["content"] == "<p>text post body</p>"
     assert calls == ["1001"]
+    # Outcome reports the captured body's shape (detail-fetched here).
+    assert rec.body_chars == len("<p>text post body</p>")
 
 
 def test_write_post_record_none_without_post_id(tmp_path):
@@ -661,4 +665,6 @@ def test_write_post_record_none_without_post_id(tmp_path):
         images_root=tmp_path, cookies_path=None, validate=False,
         session=_FakeSession(),
     )
-    assert dl.write_post_record({"id": "", "attributes": {}}, "artist-x") is None
+    rec = dl.write_post_record({"id": "", "attributes": {}}, "artist-x")
+    assert rec.path is None
+    assert rec.body_chars == 0