Address code review: fix imports, salt hashing, conditional delivery message

- Move asyncio import to module level in gmail_service.py
- Move datetime import to module level in providers.py
- Use hashlib.sha256 for per-user salt generation (no truncation risk)
- Make delivery method message conditional in AddMailAccountModal

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
Agent-Logs-Url: https://github.com/christianlouis/pop_puller_to_gmail/sessions/de3ef930-a980-4958-8a9d-a2c802918e81

backend/app/services/gmail_service.py

@@ -5,6 +5,7 @@ Uses the Gmail API's users.messages.insert() method to inject emails
 into a user's Gmail account, preserving original headers and metadata.
 This is preferred over SMTP forwarding as it doesn't modify the email.
 """
+import asyncio
 import base64
 import logging
 from typing import Optional, Dict, Any
@@ -94,8 +95,6 @@ class GmailService:
         Raises:
             GmailInjectionError: If injection fails
         """
-        import asyncio
-
         if label_ids is None:
             label_ids = ["INBOX"]
 
@@ -145,8 +144,6 @@ class GmailService:
         Returns:
             True if credentials are valid and can access Gmail
         """
-        import asyncio
-
         loop = asyncio.get_event_loop()
 
         try:
@@ -170,8 +167,6 @@ class GmailService:
         Returns:
             Email address string or None if unavailable
         """
-        import asyncio
-
         loop = asyncio.get_event_loop()
 
         try: