⬆️ chore(react-components): upgrade to React 19, drop old tests

[acasazza]

Summary

Upgrade @commercelayer/react-components from React 18 to React 19, remove all existing specs, and write new ones incrementally alongside each core/hooks feature.

Motivation

The hooks package targets React 19. Having react-components on React 18 causes a duplicate React instance error in tests. Aligning on React 19 across the whole v5 monorepo is cleaner than patching the mismatch.

Old tests were written against React 18 patterns and the legacy reducer architecture — not worth migrating. New tests will be written progressively as features land.

Tasks

• Upgrade react, react-dom devDependencies to React 19
• Upgrade @types/react, @types/react-dom to React 19 compatible versions
• Update peerDependencies to react: >=19.0.0
• Fix any TypeScript errors from React 19 type changes
• Delete all files under specs/ (except utils/ helpers and mocks/)
• Update pnpm-lock.yaml

Notes

New tests will be added per feature as part of subsequent issues (starting with #727).

References

• Blocks: feat(core,hooks): add SKU resource and useSkus hook #720, ✨ feat(SkusContainer): use useSkus hook and remove API calls from SkuReducer #727
• packages/react-components/package.json
• packages/react-components/specs/