Add Railway production deploy workflow triggered by version tags

[Copilot]

Decouples production deployment from push-to-master. Deployment now triggers only when a version tag is pushed, giving explicit control over releases.

Flow: push to master → CI runs tests → create tag v* → deploy to Railway production.

Changes

• New workflow .github/workflows/deploy-production.yml triggered on push.tags: v*
• Runs full test suite (flake8 + pytest) before deploying
• Deploys via Railway CLI using RAILWAY_TOKEN and RAILWAY_SERVICE_ID secrets

Required setup

• Add RAILWAY_TOKEN (deploy token) and RAILWAY_SERVICE_ID secrets in GitHub
• Disable auto-deploy from master in Railway dashboard

Usage

git tag v1.2.0
git push origin v1.2.0

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