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/database.py

@@ -1,12 +1,12 @@
 # app/database.py
 
-import os
 import logging
+import os
 
 from sqlalchemy import create_engine, exc
+from sqlalchemy.engine.url import make_url
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import sessionmaker
-from sqlalchemy.engine.url import make_url
 
 from app.config import settings
 
@@ -31,7 +31,7 @@ def init_db():
     if url.get_backend_name() == "sqlite":
         # 2. Extract the database path from the URL
         database_path = url.database  # e.g. "/workdir/db/database.db" or ":memory:"
-        
+
         if database_path != ":memory:":
             # 3. Ensure directory exists
             db_dir = os.path.dirname(database_path)
@@ -43,7 +43,7 @@ def init_db():
             if not os.path.exists(database_path):
                 logger.info(f"Creating new SQLite database file at {database_path}")
                 open(database_path, "a").close()
-    
+
     # 5. Now create tables if they don't exist yet
     try:
         Base.metadata.create_all(bind=engine)