infra: deploy UCMS backend to Railway with Docker Hub CI/CD

[ikennot]

Type of Change

• feat — new feature
• fix — bug fix
• chore — maintenance, dependencies, config
• docs — documentation only
• refactor — code change that neither fixes a bug nor adds a feature
• test — adding or updating tests

Labels

p1-high chore infra

What Changed

• Added Dockerfile with multi-stage build (JDK build → JRE runtime)
• Added application-prod.yaml profile (no debug logging, ddl-auto=none, HikariCP tuned)
• Added GET /api/health endpoint — returns 200 { status: UP, timestamp }, no auth required
• Added .github/workflows/docker-publish.yml — builds and pushes kenz2025/ucms-backend:latest to Docker Hub on push to main or development
• Added railway.toml for Railway deployment config
• Documented all required environment variables and deployment steps in README.md
• Added full Postman collection (docs/postman/UCMS-Full.postman_collection.json)

Why

Deploy the UCMS backend to production on Railway. The service must connect to the shared Supabase project, run Flyway migrations automatically on startup, and expose a health check endpoint for platform monitoring.

How to Test

1. Hit the health endpoint: GET https://ucms-backend-production-bc69.up.railway.app/api/health — should return 200 { "status": "UP" }
2. Import docs/postman/UCMS-Full.postman_collection.json and set base_url to https://ucms-backend-production-bc69.up.railway.app
3. Run Register → Login → Create Ticket → List Tickets

Related Issues

Closes #infra/deployment

Checklist

• Code follows the Google Java Style Guide
• No business logic in controllers
• Ownership + role checks are in the service layer
• All responses use ApiResponse<T> wrapper
• No secrets or credentials committed
• application.yaml is NOT staged
• CI passes