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/views/dropbox.py

@@ -1,12 +1,14 @@
 """
 Dropbox integration views for setup and OAuth callback.
 """
+
 from fastapi import Request
 
-from app.views.base import APIRouter, templates, require_login, settings
+from app.views.base import APIRouter, require_login, settings, templates
 
 router = APIRouter()
 
+
 @router.get("/dropbox-setup")
 @require_login
 async def dropbox_setup_page(request: Request):
@@ -15,10 +17,8 @@ async def dropbox_setup_page(request: Request):
     Shows configuration status and setup instructions.
     """
     # Check Dropbox configuration
-    is_configured = bool(settings.dropbox_app_key and 
-                         settings.dropbox_app_secret and 
-                         settings.dropbox_refresh_token)
-    
+    is_configured = bool(settings.dropbox_app_key and settings.dropbox_app_secret and settings.dropbox_refresh_token)
+
     return templates.TemplateResponse(
         "dropbox.html",
         {
@@ -27,10 +27,11 @@ async def dropbox_setup_page(request: Request):
             "app_key_value": settings.dropbox_app_key or "",
             "app_secret_value": settings.dropbox_app_secret if settings.dropbox_app_secret else "",
             "refresh_token_value": settings.dropbox_refresh_token if settings.dropbox_refresh_token else "",
-            "folder_path": settings.dropbox_folder or "/Documents/Uploads"  # Default folder path
-        }
+            "folder_path": settings.dropbox_folder or "/Documents/Uploads",  # Default folder path
+        },
     )
 
+
 @router.get("/dropbox-callback")
 @require_login
 async def dropbox_callback(request: Request, code: str = None, error: str = None):
@@ -39,27 +40,23 @@ async def dropbox_callback(request: Request, code: str = None, error: str = None
     Automatically exchanges the code for a token and saves it to the configuration.
     """
     if error:
-        return templates.TemplateResponse(
-            "dropbox_callback_error.html",
-            {"request": request, "error": error}
-        )
-    
+        return templates.TemplateResponse("dropbox_callback_error.html", {"request": request, "error": error})
+
     if not code:
         return templates.TemplateResponse(
-            "dropbox_callback_error.html",
-            {"request": request, "error": "No authorization code received from Dropbox"}
+            "dropbox_callback_error.html", {"request": request, "error": "No authorization code received from Dropbox"}
         )
-    
+
     # Display the processing page with automatic token exchange
     # Note: We provide empty strings for app_key_value and app_secret_value
     # to prevent overriding what's in sessionStorage
     return templates.TemplateResponse(
         "dropbox_callback.html",
         {
-            "request": request, 
+            "request": request,
             "code": code,
             "app_key_value": "",  # The callback will prioritize sessionStorage values
             "app_secret_value": "",  # The callback will prioritize sessionStorage values
-            "folder_path": ""  # The callback will prioritize sessionStorage values
-        }
+            "folder_path": "",  # The callback will prioritize sessionStorage values
+        },
     )