deploy-launcher.sh: omitting `EXTERNAL_SSH_PORT` produces `--port tcp::22` and an opaque vmm-cli traceback

[barakeinav1]

Background

configs/sgx.env and configs/kms.env label EXTERNAL_SSH_PORT as "SSH ports (only for dev images)", so an operator deploying a production image reasonably removes it. deploy-launcher.sh then emits --port tcp::22 and vmm-cli dies with:

ValueError: invalid literal for int() with base 10: ''

The error names neither the variable nor the cause, and deploy-launcher-guide.md does not say the value is required.

Acceptance Criteria

• deploy-launcher.sh appends the SSH --port flag only when EXTERNAL_SSH_PORT is non-empty (so the "only for dev images" comment becomes true)
• Alternatively, if it stays mandatory: the script fails with a named error and the comment says it is required on prod images too

Resources & Additional Notes

• Hit while redeploying our testnet node on a production image (dstack-0.5.8), where no sshd runs inside the CVM and the forward is inert.