Fix React example version mismatch

[tolgahan-arikan]

Summary

• Pin react and react-dom to the same exact version in all browser examples.
• Refresh the lockfile so the examples resolve react-dom@19.2.7 with react@19.2.7.
• Add a Dependabot react-runtime group so React runtime/type packages update together.
• Extend check:package-versions to fail CI if browser examples drift back to mismatched or ranged React runtime versions.

Root cause

The deployed React example resolved react@19.2.7 with react-dom@19.2.6, which React rejects at startup. The app rendered a blank root and logged the React version mismatch error.

Validation

• In-app Browser local repro before fix: blank page with react: 19.2.7 / react-dom: 19.2.6 console error.
• In-app Browser local verification after fix: Wallet Demo renders and fresh console logs are empty.
• pnpm check:package-versions
• pnpm test
• pnpm build
• pnpm build:example
• pnpm build:wagmi-example
• pnpm build:trails-actions-example

[claude]

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