Add testlogin deployment workflow

[hg1g]

Summary

Deploy configuration for testing Hanko SSO at testlogin.fair.hotosm.org.

Depends on: #492 (Hanko SSO Authentication)

Files

• .github/workflows/deploy-login-hanko.yml - GitHub Actions workflow
• compose.test.yaml - Docker compose for testing
• nginx.conf - Nginx configuration
• frontend/Dockerfile.dev - Dev container
• frontend/Dockerfile.prod - Production container
• frontend/entrypoint.sh - Dev entrypoint
• frontend/docker-entrypoint.sh - Prod entrypoint
• backend/Dockerfile.API - Adds git dependency

Deploy Target

• URL: testlogin.fair.hotosm.org
• Trigger: Push to login_hanko branch or manual dispatch