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/tasks/upload_to_s3.py

@@ -1,12 +1,14 @@
 #!/usr/bin/env python3
 
-import os
 import logging
+import os
+
 import boto3
 from botocore.exceptions import ClientError
+
+from app.celery_app import celery
 from app.config import settings
 from app.tasks.retry_config import BaseTaskWithRetry
-from app.celery_app import celery
 from app.utils import log_task_progress
 
 logger = logging.getLogger(__name__)
@@ -76,12 +78,7 @@ def upload_to_s3(self, file_path: str, file_id: int = None):
             extra_args["ACL"] = settings.s3_acl
 
         # Upload file
-        s3_client.upload_file(
-            file_path,
-            settings.s3_bucket_name,
-            s3_key,
-            ExtraArgs=extra_args
-        )
+        s3_client.upload_file(file_path, settings.s3_bucket_name, s3_key, ExtraArgs=extra_args)
 
         # Generate URL to the file (useful for public files)
         # For private files, this is just a reference and won't be accessible directly