Fix: IMAP over SSL connected without TLS; never lose a sent message's copy

v1.3.26's IMAP4_SSL subclass put its create_client ahead of aioimaplib's,
which is where the TLS context is made — so port 993 got plain TCP, the
server waited for a handshake, and every SSL account timed out ("Can't
reach the mail server"). The context is now made in our create_client too,
and a test checks an SSL client really gets one (it fails without the fix).

With IMAP down, a send could still be delivered by SMTP while filing its copy
in Sent failed — the send then counted as done and the copy was lost. The
copy is now kept and filed by file_sent_copy_job, retried (arq Retry) for
about 24 hours, then shown in Sent as usual.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/app/providers/imap_smtp/provider.py

@@ -11,6 +11,7 @@ from __future__ import annotations
 import asyncio
 import contextlib
 import re
+import ssl
 from collections.abc import AsyncIterator
 from dataclasses import dataclass
 from datetime import date
@@ -67,6 +68,11 @@ class _KeepConnectTask:
     def create_client(  # type: ignore[no-untyped-def]
         self, host, port, loop, conn_lost_cb=None, ssl_context=None
     ) -> None:
+        # This replaces IMAP4_SSL.create_client too (it comes first in the MRO),
+        # so do its one job here: without a context the connection is plain
+        # TCP to port 993, and the server just waits for a TLS handshake.
+        if ssl_context is None and isinstance(self, aioimaplib.IMAP4_SSL):
+            ssl_context = ssl.create_default_context(ssl.Purpose.SERVER_AUTH)
         local_loop = loop if loop is not None else asyncio.get_running_loop()
         self.protocol = aioimaplib.IMAP4ClientProtocol(local_loop, conn_lost_cb)
         self.connect_task = local_loop.create_task(