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/__init__.py

@@ -1,21 +1,24 @@
 """
 API Router module that combines all API endpoints
 """
-from fastapi import APIRouter
+
 import logging
 
+from fastapi import APIRouter
+
+from app.api.azure import router as azure_router
+from app.api.diagnostic import router as diagnostic_router
+from app.api.dropbox import router as dropbox_router
+from app.api.files import router as files_router
+from app.api.google_drive import router as google_drive_router
+from app.api.logs import router as logs_router
+from app.api.onedrive import router as onedrive_router
+from app.api.openai import router as openai_router
+from app.api.process import router as process_router
+from app.api.settings import router as settings_router
+
 # Import all the individual routers
 from app.api.user import router as user_router
-from app.api.files import router as files_router
-from app.api.process import router as process_router
-from app.api.diagnostic import router as diagnostic_router
-from app.api.onedrive import router as onedrive_router
-from app.api.dropbox import router as dropbox_router
-from app.api.openai import router as openai_router
-from app.api.azure import router as azure_router
-from app.api.google_drive import router as google_drive_router
-from app.api.logs import router as logs_router
-from app.api.settings import router as settings_router
 
 # Set up logging
 logger = logging.getLogger(__name__)