fix: RESET_PERSON now deletes managed Frigate files before clearing tracker

Previously reset_person wiped the local tracker but left existing Frigate
training files as orphans, causing the next run to upload a full new batch
on top of them. Now deletes all winnow-managed files from Frigate first so
the next run starts truly clean. Manually-added Frigate files are never
touched.

Also fixes a spurious warning when FRIGATE_URL is unset: the deletion step
is now skipped at info level rather than logging a misleading error. Moves
the deferred import to top-level and eliminates a double disk read.

Bumps to 0.4.1. Also fixes ruff lint violations in executor.py (import
sort, line length) and promotes the "winnow only touches files it uploaded"
callout to the README intro.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

winnow/executor.py

@@ -13,7 +13,12 @@ from rich import print as rprint
 from rich.progress import BarColumn, Progress, SpinnerColumn, TaskProgressColumn, TextColumn
 
 from .config import Config, get_headers
-from .frigate_api import delete_frigate_person_files, get_all_frigate_person_files, get_frigate_person_files, recognize_face
+from .frigate_api import (
+    delete_frigate_person_files,
+    get_all_frigate_person_files,
+    get_frigate_person_files,
+    recognize_face,
+)
 from .image_processing import process_face_mode, process_full_mode, process_object_mode
 from .immich_api import fetch_face_data, fetch_full_image
 from .log_config import console
@@ -479,7 +484,8 @@ def upload_to_frigate(jobs: list[dict]) -> None:
                             remove_frigate_file(name, target_frigate_file)
                             person_has_fscores = has_frigate_scores(name)
                             effective_count -= 1
-                            min_quality_score_for_slot = None  # clear any blur-mode slot floor — Frigate uses a different score metric
+                            # clear any blur-mode slot floor — Frigate uses a different score metric
+                            min_quality_score_for_slot = None
                         else:
                             logger.warning(f"Failed to delete {target_frigate_file} for {name}, skipping replacement")
                             failed_deletes.add(target_frigate_file)