Improve README documentation and onboarding experience

## Description

The current README can be improved to make the project more approachable for new users and contributors.

## Tasks

- [ ] Add a project architecture diagram
- [ ] Improve the installation instructions
- [ ] Add a Quick Start section
- [ ] Document environment variables
- [ ] Add usage examples
- [ ] Improve troubleshooting guidance
- [ ] Fix grammar and formatting where needed

## Acceptance Criteria

- README is easy to follow for first-time users.
- All setup steps are accurate.
- Documentation is consistent and well-formatted.

## Labels

documentation
good first issue
help wanted

Start by reviewing the current README and the project's installation and environment-variable setup. Update the README with the requested architecture diagram, Quick Start, usage examples, troubleshooting guidance, and grammar fixes; done means first-time users can follow accurate, consistent setup instructions.

Written by the indexing model from the issue text.