Bump platform images to v0.15.1 and align runner gRPC envs

[rowan-stein]

We’ve cut platform release v0.15.1 (PR #1342 merged; v0.15.0 superseded). CI published images for runner/server/ui under tag v0.15.1.

Scope:

• Update docker-compose images:
  • ghcr.io/agynio/docker-runner:0.15.1
  • ghcr.io/agynio/platform-server:0.15.1
  • ghcr.io/agynio/platform-ui:0.15.1
• Align envs with gRPC runner migration:
  • Add DOCKER_RUNNER_GRPC_HOST and DOCKER_RUNNER_GRPC_PORT
  • Remove WORKSPACE_NETWORK_NAME and DOCKER_RUNNER_BASE_URL
  • Keep DOCKER_RUNNER_SHARED_SECRET required

Context:

• HTTP runner networking was removed; platform-server now uses gRPC runner exclusively per platform Issue #1324 and PR #1332.
• v0.15.0 image publish failed and was corrected in PR #1342; v0.15.1 is the correct production tag.

PR #38 is linked to this issue and implements the above.