docs: add defineNitroPlugin to migration guide

[RihanArfan]

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Adds missing plugin section to migration guide

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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Project	Deployment	Actions	Updated (UTC)
nitro.build	Ready	Preview, Comment	Jul 1, 2026 11:51am

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 8e26b529-6158-4cf1-b234-441588e1e0e9

📥 Commits

Reviewing files that changed from the base of the PR and between ad3a2d4 and ba457c7.

📒 Files selected for processing (1)

• docs/1.docs/99.migration.md

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📝 Walkthrough

Walkthrough

Documentation update adding a "Plugins" section to the Nitro v2→v3 migration guide, describing the rename of defineNitroPlugin to definePlugin with an updated code snippet showing import and usage changes.

Changes

Migration Documentation Update

Layer / File(s)	Summary
Plugins migration section docs/1.docs/99.migration.md	New "Plugins" subsection documents the defineNitroPlugin → definePlugin rename with an updated import-and-export code snippet.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• nitrojs/nitro#3857: Updates the same plugin documentation to reflect the defineNitroPlugin to definePlugin rename and example usage.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses a conventional commits prefix and accurately describes the documentation update.
Description check	✅ Passed	The description is clearly related to the migration guide documentation update.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/migration-plugin

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commit: ba457c7