fix: a game build is recognised before the archive integrity test, so re-extract no longer stalls on it

The archive probe read and checksummed every member before the importer
looked at what the archive held. For a multi-gigabyte game build that is
minutes of work on a file that is kept whole and never extracted, and it
held a re-extract chunk far past its time budget.

- The importer checks the archive's directory for a software build first,
  for the outer archive and for one nested inside an art pack, and only
  probes archives it may extract.
- The probe rejects an archive over the size cap from its directory totals,
  before the integrity test decompresses anything.
- Re-extract logs each archive as it starts and finishes, with its size and
  how long it took, so an archive that stalls a chunk is named in the log.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/app/services/cleanup_service.py

@@ -1205,6 +1205,11 @@ def reextract_archive_attachments(
         )
         if post is None:
             summary["without_post"] += 1
+        # Logged on the way in as well as out, so an archive that stalls a
+        # chunk is named in the log even if the worker dies holding it.
+        size_mb = (att.size_bytes or 0) / 1e6
+        log.info("re-extract: attachment %s (%.0f MB) starting", att.id, size_mb)
+        archive_start = time.monotonic()
         try:
             ids = _reextract_archive_to_post(
                 importer, stored, post, source_row, artist, images_root,
@@ -1214,8 +1219,11 @@ def reextract_archive_attachments(
         except Exception as exc:  # one bad archive must not strand the rest
             session.rollback()
             summary["errors"] += 1
-            log.warning("re-extract failed for attachment %s: %s", att.id, exc)
+            log.warning("re-extract failed for attachment %s after %.1fs: %s",
+                        att.id, time.monotonic() - archive_start, exc)
             continue
+        log.info("re-extract: attachment %s done in %.1fs, %d new image(s)",
+                 att.id, time.monotonic() - archive_start, len(ids))
         if ids:
             summary["members_imported"] += len(ids)
             if post is not None: