fix: restore missing forward_email signature and reformat with black

Agent-Logs-Url: https://github.com/christianlouis/InboxConverge/sessions/3c4ae596-6052-4a61-9edd-b668a6cda32e

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/app/services/mail_processor.py

@@ -432,9 +432,7 @@ class MailProcessor:
 
         return emails, new_uids
 
-    async def post_process_imap(
-        self, successfully_forwarded_uids: List[str]
-    ) -> None:
+    async def post_process_imap(self, successfully_forwarded_uids: List[str]) -> None:
         """Mark successfully forwarded IMAP messages as \\Seen and optionally delete.
 
         Because fetch uses ``BODY.PEEK[]`` (which does NOT set \\Seen), this
@@ -485,9 +483,7 @@ class MailProcessor:
                 except Exception:
                     pass
 
-    async def post_process_pop3(
-        self, successfully_forwarded_uids: List[str]
-    ) -> None:
+    async def post_process_pop3(self, successfully_forwarded_uids: List[str]) -> None:
         """Delete successfully forwarded POP3 messages from the source mailbox.
 
         Opens a fresh POP3 session, maps stable UIDs back to current message
@@ -569,7 +565,8 @@ class MailProcessor:
         else:
             await self.post_process_imap(successfully_forwarded_uids)
 
-
+    @staticmethod
+    async def forward_email(
         email_data: bytes,
         source_account_name: str,
         destination: str,