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/files.py

@@ -2,13 +2,14 @@
 File management views for displaying and managing files.
 """
 
-from fastapi import Request, Depends, Query
-from sqlalchemy.orm import Session
 from typing import Optional
 
-from app.views.base import APIRouter, templates, require_login, get_db, logger
-from app.utils.file_status import get_files_processing_status
+from fastapi import Depends, Query, Request
+from sqlalchemy.orm import Session
+
 from app.config import settings
+from app.utils.file_status import get_files_processing_status
+from app.views.base import APIRouter, get_db, logger, require_login, templates
 
 router = APIRouter()
 
@@ -31,8 +32,9 @@ def files_page(
     """
     try:
         # Import the model here to avoid circular imports
+        from sqlalchemy import asc, desc, or_
+
         from app.models import FileRecord, ProcessingLog
-        from sqlalchemy import desc, asc, or_
 
         # Start with base query
         query = db.query(FileRecord)
@@ -159,9 +161,10 @@ def file_detail_page(request: Request, file_id: int, db: Session = Depends(get_d
     Return the file detail page showing processing history and file information
     """
     try:
-        from app.models import FileRecord, ProcessingLog
         import os
 
+        from app.models import FileRecord, ProcessingLog
+
         # Find the file record
         file_record = db.query(FileRecord).filter(FileRecord.id == file_id).first()