fix: roll back IB Gateway image with unready API

[Pigbibi]

Evidence

• The 10.50.1d rollout started at 2026-08-25 13:28 UTC.
• API health checks were successful immediately before it and consistently timed out afterwards despite TCP reachability and successful authentication.
• The only runtime-image change was 10.48.1d to 10.50.1d.

Change

Roll back to 10.48.1d, the last verified API-ready Gateway image. The current account will be deployed through a manually selected, full deploy after CI—no fleet-wide automatic rollout.

Validation

• bash tests/test_workflow_shared_config.sh
• bash tests/test_gateway_recovery_scripts.sh
• CI Docker build pending.

[Pigbibi]

Closed after targeted runtime diagnosis: Gateway 10.48.1d reproduced the same IBKR server-disconnect login error, so an image rollback is not a verified fix. The safety fix for cancelled-deploy watcher recovery remains merged in #122.