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/uptime_kuma_tasks.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 
 import logging
+
 import requests
 from celery import shared_task
 
@@ -8,6 +9,7 @@ from app.config import settings
 
 logger = logging.getLogger(__name__)
 
+
 @shared_task
 def ping_uptime_kuma():
     """
@@ -18,7 +20,7 @@ def ping_uptime_kuma():
     if not settings.uptime_kuma_url:
         logger.debug("Uptime Kuma URL not configured, skipping ping")
         return
-    
+
     try:
         logger.info(f"Pinging Uptime Kuma at {settings.uptime_kuma_url}")
         response = requests.get(settings.uptime_kuma_url, timeout=10)