fix(vercel): pin Node.js to 20.x

[Legit-Ox]

Summary

• engines.node changed from >=20.0.0 to 20.x
• Vercel was auto-selecting Node 24, causing tree-sitter native addon (cppgc API incompatibility) build failure
• Pinning to 20.x locks Vercel to Node 20 LTS

Test plan

• Trigger Vercel deployment after merge, confirm build succeeds on Node 20

🤖 Generated with Claude Code

[github-actions]

GSSoC Label Checklist 🏷️

@Umbrella-io — 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

[Priyanshu-byte-coder]

LGTM

[github-actions]

PR is approved but missing a level:* difficulty label and gssoc:approved — add before merging so it scores in GSSoC. 🏷️

[github-actions]

🎉 Merged! Thanks for contributing to DevTrack.

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