Fix Docker startup with a fresh PostgreSQL database

[rezerov]

A fresh docker compose up --build -d can start the gateway before PostgreSQL finishes initialization, causing the gateway to crash and preventing the control plane and dashboard from starting. Make both database clients wait for a healthy PostgreSQL service, and probe PostgreSQL over TCP so its temporary Unix-socket initialization server cannot satisfy the health check.

Extend CI's container check to start the complete stack with a fresh database, probe the gateway, control plane and dashboard, and reject container restarts. The check prints logs on failure and cleans up its containers and volume.

Validation:

• Fresh database: all four services started, all three HTTP probes passed, zero container restarts.
• Existing database: recreated the stack, verified a stored sentinel row was retained, and repeated the HTTP/restart checks.
• Compose configuration, CI shell syntax and git diff --check passed.