Add v2 to v3 migration guide

[Copilot]

Documents breaking changes and upgrade path from v2 to v3. Primary breaking change is refractor/react-refractor upgrade (addressing CVE-2024-53382) with API changes affecting direct consumers.

Changes

• MIGRATION.md: Comprehensive upgrade guide covering:

  • Node.js requirement: >=14.0.0 → >=20.19.0 || >=22.12.0
  • refractor: 4.9.0 → 5.0.0, react-refractor: 2.2.0 → 4.0.0
  • API migration for direct react-refractor users (default → named exports, import path changes)
  • Step-by-step upgrade instructions

• README.md: Added migration section linking to guide

Impact

Users of @sanity/ui Code component require no code changes. Direct react-refractor consumers need to update imports:

// Before
-import Refractor from 'react-refractor'
-import javascript from 'refractor/lang/javascript'
-Refractor.registerLanguage(javascript)

// After
+import {Refractor, registerLanguage} from 'react-refractor'
+import javascript from 'refractor/javascript'
+registerLanguage(javascript)

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Project	Deployment	Actions	Updated (UTC)
sanity-ui-storybook	Error		Feb 18, 2026 2:46pm
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