fix: resolve ruff lint errors in scheduler and tests

- scheduler.py: sort import block (I001)
- tests/test_config.py: remove unused os, pytest imports (F401)
- tests/test_upload_tracker.py: remove unused json, os, tempfile imports (F401)

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

tests/test_upload_tracker.py

@@ -1,8 +1,5 @@
 """Tests for upload tracker — mark, filter, reset, and summary logic."""
 
-import json
-import os
-import tempfile
 
 import pytest