security: add X-DNS-Prefetch-Control header

[Honey-pg]

Summary

Set X-DNS-Prefetch-Control: on in next.config.mjs so the application explicitly controls DNS prefetching behavior.

Closed #2016

---

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

---

Changes Made

• Added X-DNS-Prefetch-Control: on to the global security headers in next.config.mjs

---

How to Test

1. Run npm run build (or npm run dev) and start the app
2. Open any page and inspect response headers (browser DevTools → Network → document request)
3. Confirm X-DNS-Prefetch-Control: on is present on responses

---

Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

---

Additional Notes

This is a security header addition only; no UI or API behavior changes. Note: an existing branch security/x-dns-prefetch-control uses off instead of on — confirm which value is intended before merging.

[vercel]

@Honey-pg is attempting to deploy a commit to the PRIYANSHU DOSHI's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus