Add VPS IMAP sorting automation

Prompts used since the previous commit:
- Hieronder staat je oorspronkelijke plan. Volgens mij moet stap 'Add VPS automation' nog worden uitgevoerd, inclusief de testen.

Special observations:
- Added a testable IMAP sorting daemon, shared IMAP operation helpers, systemd service template, and SSH deployment script.
- Local tests passed; no live VPS deployment or mailbox-affecting daemon test was run.
- verplaats_log.json remains modified from the user's run and was intentionally not staged.

systemd/mailcat-sort.service

@@ -0,0 +1,21 @@
+[Unit]
+Description=Mailcat IMAP sorting daemon
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=__APP_USER__
+Group=__APP_USER__
+WorkingDirectory=__APP_DIR__
+ExecStart=/usr/bin/python3 __APP_DIR__/sort_mail_daemon.py --account __ACCOUNT__ --folder INBOX --state-file /var/lib/mailcat/sort_mail_daemon_state.json --log-file /var/log/mailcat/sort_mail_daemon.log
+Restart=always
+RestartSec=30
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectSystem=full
+ProtectHome=true
+ReadWritePaths=__APP_DIR__ /var/lib/mailcat /var/log/mailcat
+
+[Install]
+WantedBy=multi-user.target