docs: refresh README accuracy

[mohosin2126]

Summary

This PR refreshes the README to better match the current state of the repository.

What changed

• Updated repository links to yeasin2002/bulletproof-nextjs-starter
• Updated the clone command and project directory name
• Removed the broken npm run setup flow from Quick Start and Available Scripts
• Added pnpm install as the recommended install path
• Updated the project structure section to match the actual repository layout
• Adjusted authentication/testing wording so it reflects the current starter/scaffolding state more accurately

Why

The previous README still referenced:

• the old repository name and links
• a setup script that does not exist
• an outdated project structure
• auth wording that implied more implementation than is currently wired in the app