[4.4] README update for deployment, env vars

[underscorekadji]

Milestone: 4 – UX Polish & NFRs
Size: S (≤ 2 hours)
Labels: docs

Description

Update README with comprehensive deployment instructions and environment variable documentation.

Acceptance Criteria

• Deployment instructions added
• Environment variables documented
• Docker deployment guide
• Production setup instructions
• Troubleshooting section
• Configuration examples

Definition of Done

• PR reviewed & merged
• GitHub Actions pipeline passes (lint → build → smoke)