fix: add ENV=production to Kubernetes deployment for secure session cookies

[Hell1213]

Description

Added ENV=production to Kubernetes deployment configuration to enable secure HTTPS-only session cookies, fixing session persistence issues.

• Fixes: I have to log in all the time #417

Checklist

• Ran npx prettier --write . (for formatting)
• Ran gofmt -w . (for Go backend)
• Ran npm test (for JS/TS testing)
• Added unit tests, if applicable
• Verified all tests pass
• Updated documentation, if needed

Additional Notes

Without ENV=production, session cookies had Secure=false, causing browsers to reject them on HTTPS sites. This resulted in users having to log in on every visit.

Changes:

• Added ENV variable to backend-env-configmap.yaml
• Added ENV reference to backend-deployment.yaml
• Updated production README with ENV configuration

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[Hell1213]

Added missing ENV=production to K8s deployment config. This enables secure cookies for HTTPS, fixing the session persistence issue where users had to log in every visit.