Improve Project Documentation for New Contributors

[avishek0769]

Summary

Upgrade docs so a new contributor can understand architecture, run project, and make first PR quickly.

Problem

README currently describes high-level concepts but lacks detailed contributor onboarding and deeper implementation references.

Expected Solution

Expand documentation with architecture diagrams, module responsibilities, setup troubleshooting, API map, and contribution workflow.

Scope

• README.md
• Optional docs/ directory (architecture, backend/frontend guides, API guides)
• Contribution templates/checklists

Acceptance Criteria

• New contributor can set up and run project using docs only.
• Docs include architecture overview and key data flow (ingestion, retrieval, chat).
• API and environment variable references are clear and current.