style: fix all flake8 linter errors across app/ directory

- Run Black formatter and isort on all app/ files
- Remove unused imports (F401) across multiple files
- Add # noqa: F401 for intentional re-exports in celery_worker.py,
  tasks/__init__.py, utils.py, frontend.py, views/base.py
- Fix f-strings without placeholders (F541) in azure.py, notification.py,
  check_credentials.py, upload_to_onedrive.py, settings.py
- Fix bare except (E722) in upload_to_sftp.py
- Fix block comment format (E265) in models.py
- Move imports to top of file to fix E402 in celery_app.py, celery_worker.py
- Fix line-too-long (E501) by wrapping strings in multiple files
- Remove unused variable (F841) in upload_to_nextcloud.py

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/utils/config_validator.py

@@ -4,29 +4,25 @@ Configuration validation for the application.
 This file serves as a backward-compatible interface to the config_validator package.
 """
 
-# Import and re-export all functions from the new package
-from app.utils.config_validator.validators import (
-    validate_email_config, 
-    validate_storage_configs, 
-    validate_notification_config,
-    check_all_configs
-)
 from app.utils.config_validator.masking import mask_sensitive_value
 from app.utils.config_validator.providers import get_provider_status
-from app.utils.config_validator.settings_display import (
-    get_settings_for_display,
-    dump_all_settings
+from app.utils.config_validator.settings_display import dump_all_settings, get_settings_for_display
+
+# Import and re-export all functions from the new package
+from app.utils.config_validator.validators import (
+    check_all_configs,
+    validate_email_config,
+    validate_notification_config,
+    validate_storage_configs,
 )
 
 __all__ = [
-    'validate_email_config',
-    'validate_storage_configs',
-    'validate_notification_config',
-    'mask_sensitive_value',
-    'get_provider_status',
-    'get_settings_for_display',
-    'dump_all_settings',
-    'check_all_configs'
+    "validate_email_config",
+    "validate_storage_configs",
+    "validate_notification_config",
+    "mask_sensitive_value",
+    "get_provider_status",
+    "get_settings_for_display",
+    "dump_all_settings",
+    "check_all_configs",
 ]
-
-