feat(patreon): structured ingester results + quarantine surfacing — #704 step 1

The native ingester faked gallery-dl stdout (`Cursor:` lines, summary) and
phase 3 regex-scraped it back — so Patreon run-stats were mostly zero and
quarantine stats blank. We own the ingester, so it now RETURNS structured
data and phase 3 reads it directly.

- DownloadResult gains run_stats/cursor/posts_processed (None/0 on the
  gallery-dl path, which keeps the text route).
- Ingester builds real run_stats from per-media outcome counts, sets the
  checkpoint cursor structurally (no fake `Cursor:` stdout), and counts
  posts processed. download_service phase 3 uses dl_result.run_stats when
  present; the backfill lifecycle + TIMEOUT→PARTIAL block checkpoint
  dl_result.cursor instead of parse_last_cursor(stdout).
- #4 quarantine: PatreonDownloader reports a distinct "quarantined"
  MediaOutcome (with the _quarantine dest); the ingester surfaces a real
  files_quarantined + quarantined_paths + run_stats.quarantined_count
  (was hardcoded 0). Quarantined media isn't written or marked seen.
- Cleanup: parse_last_cursor + _CURSOR_RE (and the now-unused `import re`)
  removed from gallery_dl — the structured cursor replaced the scrape.

Tests: ingester result carries real run_stats/cursor/posts_processed +
quarantine counts; downloader quarantines an invalid file as "quarantined";
backfill cursor tests pass cursor= structurally; dropped the
parse_last_cursor tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/services/download_service.py

@@ -33,7 +33,6 @@ from .gallery_dl import (
     ErrorType,
     GalleryDLService,
     SourceConfig,
-    parse_last_cursor,
 )
 from .importer import Importer
 from .patreon_ingester import PatreonIngester
@@ -155,7 +154,7 @@ class DownloadService:
         # timed out with NO progress stays TIMEOUT and feeds phase 3's
         # stall-guard. Leave RATE_LIMITED alone so the platform-cooldown fires.
         if in_backfill and dl_result.error_type == ErrorType.TIMEOUT:
-            new_cursor = parse_last_cursor(dl_result.stdout, dl_result.stderr)
+            new_cursor = dl_result.cursor  # plan #704: structured, not scraped
             advanced = bool(
                 (new_cursor and new_cursor != overrides.get("_backfill_cursor"))
                 or dl_result.files_downloaded > 0
@@ -439,9 +438,14 @@ class DownloadService:
             select(DownloadEvent).where(DownloadEvent.id == event_id)
         )).scalar_one()
 
-        run_stats = self.gdl._compute_run_stats(
-            dl_result.return_code, dl_result.stdout, dl_result.stderr
-        )
+        # plan #704: the native ingester returns structured run_stats; only the
+        # gallery-dl path needs the regex-over-stdout reconstruction.
+        if dl_result.run_stats is not None:
+            run_stats = dict(dl_result.run_stats)
+        else:
+            run_stats = self.gdl._compute_run_stats(
+                dl_result.return_code, dl_result.stdout, dl_result.stderr
+            )
         run_stats["quarantined_count"] = dl_result.files_quarantined
         stderr_summary = self.gdl._extract_errors_warnings(dl_result.stderr)
 
@@ -528,12 +532,12 @@ class DownloadService:
             src.backfill_runs_remaining = 0
             return
 
-        # Did not finish. Patreon checkpoints + resumes via cursor; other
-        # platforms have no resumable cursor (every chunk re-walks from the
-        # top), so they advance only by the download archive growing.
+        # Did not finish. The native ingester checkpoints + resumes via cursor
+        # (carried structurally on the result, plan #704); gallery-dl platforms
+        # have no resumable cursor (every chunk re-walks from the top), so they
+        # advance only by the download archive growing.
         new_cursor = (
-            parse_last_cursor(dl_result.stdout, dl_result.stderr)
-            if uses_native_ingester(ctx["platform"]) else None
+            dl_result.cursor if uses_native_ingester(ctx["platform"]) else None
         )
         advanced = bool(
             (new_cursor and new_cursor != old_cursor)