Add network timeouts to prevent container hangs on unreachable servers

Without timeouts, smtplib.SMTP() / imaplib.IMAP4_SSL() / paramiko.Transport()
hang indefinitely when the remote server is down or firewall-dropped, blocking
the entire background thread and eventually freezing the app.

- SMTP: 30s connect/operation timeout
- IMAP: 30s connect/operation timeout
- SFTP (paramiko): 15s socket connect, 15s banner, 30s auth
- SMB and FTP already had timeouts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/mail_processor.py

@@ -40,14 +40,18 @@ def _connect_imap(settings: dict) -> imaplib.IMAP4_SSL | imaplib.IMAP4:
 
     if use_ssl:
         ctx = ssl.create_default_context()
-        conn = imaplib.IMAP4_SSL(server, port, ssl_context=ctx)
+        conn = imaplib.IMAP4_SSL(server, port, ssl_context=ctx, timeout=IMAP_TIMEOUT)
     else:
-        conn = imaplib.IMAP4(server, port)
+        conn = imaplib.IMAP4(server, port, timeout=IMAP_TIMEOUT)
 
     conn.login(settings["imap_username"], settings["imap_password"])
     return conn
 
 
+SMTP_TIMEOUT = 30  # seconds - prevents hangs when SMTP server is unreachable
+IMAP_TIMEOUT = 30  # seconds
+
+
 def _connect_smtp(settings: dict) -> smtplib.SMTP | smtplib.SMTP_SSL:
     server = settings["smtp_server"]
     port = int(settings.get("smtp_port", 587))
@@ -55,9 +59,9 @@ def _connect_smtp(settings: dict) -> smtplib.SMTP | smtplib.SMTP_SSL:
 
     if mode == "ssl":
         ctx = ssl.create_default_context()
-        conn = smtplib.SMTP_SSL(server, port, context=ctx)
+        conn = smtplib.SMTP_SSL(server, port, context=ctx, timeout=SMTP_TIMEOUT)
     else:
-        conn = smtplib.SMTP(server, port)
+        conn = smtplib.SMTP(server, port, timeout=SMTP_TIMEOUT)
         if mode == "starttls":
             ctx = ssl.create_default_context()
             conn.starttls(context=ctx)