Refresh Postgres migration runtime (#35)

[AntoineToussaint]

Closes #35.

Summary

• Replaces the obsolete migration binary whose Go runtime crashes in supported k3d environments.
• Pins generated bootstrap images to the same current golang-migrate release used by the agent library.
• Publishes the fix as an immutable Postgres agent patch for downstream GitOps snapshots.

Test plan

• go test ./...
• git diff --check
• Signed release commit verified with git verify-commit
• Live Mind k3d topology reproduced the v4.15.0 runtime crash after successful PostgreSQL connectivity