feat(go-api): Dockerfile for Go API service

[Depo-dev]

Summary

No Dockerfile exists for the Go API service. The production docker-compose.yml references a build at services/api.

Acceptance Criteria

• Multi-stage Dockerfile: builder (golang:1.22-alpine) + runtime (alpine:3.19)
• Builder: go build -o /api ./...
• Runtime: copy binary only, run as non-root user
• Exposes PORT (default 3000)
• Final image < 30 MB
• docker build succeeds locally and in CI

Files

services/api/Dockerfile (new)