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/api/user.py

@@ -1,15 +1,18 @@
 """
 User-related API endpoints
 """
-from fastapi import APIRouter, Request, HTTPException
-from hashlib import md5
+
 import logging
+from hashlib import md5
+
+from fastapi import APIRouter, HTTPException, Request
 
 # Set up logging
 logger = logging.getLogger(__name__)
 
 router = APIRouter()
 
+
 async def whoami_handler(request: Request):
     """
     Returns user info if logged in, else 401.
@@ -26,18 +29,20 @@ async def whoami_handler(request: Request):
     # MD5 is used here for Gravatar's URL generation (not for security), so usedforsecurity=False
     email_hash = md5(email.strip().lower().encode(), usedforsecurity=False).hexdigest()
     gravatar_url = f"https://www.gravatar.com/avatar/{email_hash}?d=identicon"
-    
+
     # Add the gravatar URL to the user object instead of creating a new response
     user_response = user.copy()  # Create a copy to avoid modifying the session
     user_response["picture"] = gravatar_url
-    
+
     return user_response
 
+
 # Register the same handler under two different paths
 @router.get("/whoami")
 async def whoami(request: Request):
     return await whoami_handler(request)
 
+
 @router.get("/auth/whoami")
 async def auth_whoami(request: Request):
     return await whoami_handler(request)