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/utils/encryption.py

@@ -5,9 +5,9 @@ Uses Fernet symmetric encryption with a key derived from SESSION_SECRET.
 This provides encryption at rest for sensitive configuration values.
 """
 
-import logging
 import base64
 import hashlib
+import logging
 from typing import Optional
 
 logger = logging.getLogger(__name__)
@@ -19,33 +19,34 @@ _cipher_suite = None
 def _get_cipher_suite():
     """
     Get or create the Fernet cipher suite for encryption/decryption.
-    
+
     The encryption key is derived from SESSION_SECRET to ensure:
     1. Settings are encrypted at rest in the database
     2. The same key is used across app restarts
     3. No additional secret management needed
-    
+
     Returns:
         Fernet cipher suite instance
     """
     global _cipher_suite
-    
+
     if _cipher_suite is None:
         try:
             from cryptography.fernet import Fernet
+
             from app.config import settings
-            
+
             # Derive a Fernet-compatible key from SESSION_SECRET
             # Fernet requires a 32-byte base64-encoded key
-            secret = settings.session_secret.encode('utf-8')
-            
+            secret = settings.session_secret.encode("utf-8")
+
             # Use SHA256 to get exactly 32 bytes, then base64 encode
             key_bytes = hashlib.sha256(secret).digest()
             fernet_key = base64.urlsafe_b64encode(key_bytes)
-            
+
             _cipher_suite = Fernet(fernet_key)
             logger.debug("Encryption cipher suite initialized")
-            
+
         except ImportError:
             logger.warning(
                 "cryptography library not installed. "
@@ -56,34 +57,34 @@ def _get_cipher_suite():
         except Exception as e:
             logger.error(f"Failed to initialize encryption: {e}")
             _cipher_suite = None
-    
+
     return _cipher_suite
 
 
 def encrypt_value(plaintext: Optional[str]) -> Optional[str]:
     """
     Encrypt a plaintext value for storage in the database.
-    
+
     Args:
         plaintext: The value to encrypt (or None)
-        
+
     Returns:
         Encrypted value as base64 string, or plaintext if encryption unavailable
     """
     if plaintext is None or plaintext == "":
         return plaintext
-    
+
     cipher = _get_cipher_suite()
-    
+
     if cipher is None:
         # Encryption not available, store in plaintext with warning
         logger.warning("Storing sensitive value in plaintext (encryption unavailable)")
         return plaintext
-    
+
     try:
-        encrypted_bytes = cipher.encrypt(plaintext.encode('utf-8'))
+        encrypted_bytes = cipher.encrypt(plaintext.encode("utf-8"))
         # Prefix with "enc:" to identify encrypted values
-        return "enc:" + encrypted_bytes.decode('utf-8')
+        return "enc:" + encrypted_bytes.decode("utf-8")
     except Exception as e:
         logger.error(f"Encryption failed: {e}")
         # Fall back to plaintext
@@ -93,32 +94,32 @@ def encrypt_value(plaintext: Optional[str]) -> Optional[str]:
 def decrypt_value(ciphertext: Optional[str]) -> Optional[str]:
     """
     Decrypt a value from the database.
-    
+
     Args:
         ciphertext: The encrypted value (or plaintext if not encrypted)
-        
+
     Returns:
         Decrypted plaintext value
     """
     if ciphertext is None or ciphertext == "":
         return ciphertext
-    
+
     # Check if value is encrypted (has "enc:" prefix)
     if not ciphertext.startswith("enc:"):
         # Not encrypted, return as-is
         return ciphertext
-    
+
     cipher = _get_cipher_suite()
-    
+
     if cipher is None:
         logger.error("Cannot decrypt value: encryption not available")
         return "[ENCRYPTED - Cannot decrypt]"
-    
+
     try:
         # Remove "enc:" prefix and decrypt
-        encrypted_bytes = ciphertext[4:].encode('utf-8')
+        encrypted_bytes = ciphertext[4:].encode("utf-8")
         plaintext_bytes = cipher.decrypt(encrypted_bytes)
-        return plaintext_bytes.decode('utf-8')
+        return plaintext_bytes.decode("utf-8")
     except Exception as e:
         logger.error(f"Decryption failed: {e}")
         return "[DECRYPTION FAILED]"
@@ -127,10 +128,10 @@ def decrypt_value(ciphertext: Optional[str]) -> Optional[str]:
 def is_encrypted(value: Optional[str]) -> bool:
     """
     Check if a value is encrypted.
-    
+
     Args:
         value: The value to check
-        
+
     Returns:
         True if the value is encrypted, False otherwise
     """
@@ -140,7 +141,7 @@ def is_encrypted(value: Optional[str]) -> bool:
 def is_encryption_available() -> bool:
     """
     Check if encryption is available.
-    
+
     Returns:
         True if cryptography library is installed and encryption is working
     """