chore: upgrade Next.js to 15.5.6 and React to stable 19.2.0

[pandaabinash99]

Summary:

Upgraded the project dependencies to align with the latest stable versions of React and Next.js for improved performance, stability, and long-term compatibility.

• Updated React and React DOM from 19.0.0-rc-69d4b800-20241021 → 19.0.0
• Updated Next.js from 15.0.1 → 15.5.6
• Reinstalled dependencies and updated lock file
• Verified local build and dev server

Issue Link:

Fixes #134

PR Checks:

• Code is properly formatted (executed make pre-push command).
• No ESLint warnings (verified with make pre-push command).
• UI Changes are responsive (checked in the responsive view).
• Performance is maintained (Lighthouse report reviewed).
• User experience (UX) considerations are met.
• Accessibility is supported (validated with accessibility tools).

[pandaabinash99]

@RajatRajdeep upgraded react and react-dom to 19.2.0.