feat: write README with full setup and contribution guide

[dzekojohn4]

Task

Update README.md with complete documentation.

Sections to include

1. Project overview
2. Tech stack
3. Getting started (clone, install, env setup, run)
4. Project structure explanation
5. Available scripts
6. Environment variables table
7. Contributing guide (branch naming, PR process)
8. Architecture overview (pages, stores, services flow)

Acceptance Criteria

• README covers all sections above
• Setup instructions work end-to-end
• Contributing guide is clear for new contributors