docs: add website screenshots to README

[saurabhhhcodes]

Summary

• replace the README screenshot placeholder with real project previews
• add captured screenshots for the home, voice assistant, crop analysis, and market prices pages
• keep the change scoped to documentation and static assets

Closes #70

Verification

• npm run type-check
• git diff --check
• captured screenshots from the local Next.js app at http://127.0.0.1:3037

[vercel]

@saurabhhhcodes is attempting to deploy a commit to the ashishparab03-gmailcom's projects Team on Vercel.

A member of the Team first needs to authorize it.

[saurabhhhcodes]

Hi @asheesh109, this PR is ready for review. Could you please add the GSSoC scoring labels if the change looks good?

Suggested labels:

• gssoc:approved
• level:beginner
• type:documentation

Verification completed:

• npm run type-check
• git diff --check

Note: the Vercel statuses are failing at the repository authorization step, not from the code change.