Proxy `run-docker.sh` to `flagsmith` entrypoint

[khvn26]

Replace run-docker.sh with the flagsmith CLI entrypoint.

Acceptance criteria

• The flagsmith-common release that ships Replace Core's run-docker.sh flagsmith-common#239 is pulled in.
• Container images start via the flagsmith entrypoint, with run-docker.sh reduced to a thin shim, without breaking existing ECS task definitions or compose files.
• Migrations run once per deploy — the task processor no longer migrates on each task start.
• The temporary health-check startPeriod raised in fix(infra): Task processor tasks killed during startup by health check #7887 is reverted.
• In-repo references to run-docker.sh and its startup verbs (docker-compose files, Dockerfile) are updated.