docs: update outdated tech stack and incorrect test commands

[root-sarvesh]

This PR updates outdated documentation in README.md and docs/DEV.md to match the current codebase and tooling.

Summary of Changes

• Updated tech stack details to reflect actual versions used (TypeScript 5, React 18, Vite 6, Vitest).
• Removed outdated references to Jest and Cypress.
• Replaced incorrect test commands (test:unit, test:e2e) with the correct npm run test instruction.
• Clarified that the project uses Vitest for unit tests.
• Updated DEV.md to remove non-existent scripts and prevent setup confusion.

Scope

• Documentation-only changes

• Two files updated:

   1.    README.md
  
   2.    docs/DEV.md
  

Reason

The existing docs contained outdated tooling and commands that no longer match the repository’s current structure or scripts. This update helps new contributors avoid setup errors and aligns documentation with the actual monorepo environment.

Testing

Verified that updated commands (npm run test) work as documented.

Fixes #471