fix: raise imaplib line limit for large mailboxes (#2895)

Python's imaplib._MAXLINE defaults to 1 MB. Mailboxes with tens of
thousands of messages exceed this on UID SEARCH ALL, crashing with
'got more than 1000000 bytes'.

Set _MAXLINE to 50 MB after opening the connection so large mailboxes
work without error.

Fixes #2883

Co-authored-by: michaelxer <michaelxer@users.noreply.github.com>

routes/email_helpers.py

@@ -714,6 +714,10 @@ def _open_imap_connection(host: str, port: int, *, starttls: bool, timeout: int
         conn.sock.settimeout(timeout)
     except Exception:
         pass
+    # Raise the IMAP line-length limit from the default 1 MB to 50 MB so that
+    # large mailboxes (tens of thousands of messages) don't crash with
+    # "got more than 1000000 bytes" on UID SEARCH ALL.  (#2883)
+    imaplib._MAXLINE = 50_000_000
     return conn
 
 def _imap_connect(account_id: str | None = None, owner: str = ""):