docs: fix local dev instructions for Mintlify

[kashish00208]

Description

Fixes #12267

The current contributing guide suggests using npm run dev, which does not work reliably due to Mintlify CLI issues with local installs.

This updates the instructions to use the global CLI (mint dev), which is currently the only stable method.

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Checklist

• I've read the contributing guide

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Summary by cubic

Switch local docs dev to the global mint CLI: run mint dev instead of npm run dev to avoid issues with local installs. Fixes #12267.

• Migration
  • Install mint globally: npm install -g mint
  • Start docs: mint dev

^{Written for commit 7495f91. Summary will update on new commits.}

[github-actions]

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[cubic-dev-ai]

No issues found across 1 file

[kashish00208]

I have read the CLA Document and I hereby sign the CLA