fix: address 3 quality review findings — record_frigate_files_batch cache mutation, tracker_ok flag, LIMIT guard

- record_frigate_files_batch: copy-before-mutate so a write failure
  doesn't leave cache ahead of disk (same fix as remove_frigate_files_batch)
- executor: replace tracker_ok boolean with try/else
- jobs: collapse duplicate custom_limit is not None checks into one guard

Bump version to 0.6.3.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "winnow"
-version = "0.6.2"
+version = "0.6.3"
 description = "Selects diverse, high-quality photos from Immich as training data for Frigate face recognition."
 license = "AGPL-3.0-or-later"
 requires-python = ">=3.13"