refactor(create-vite): migrate tseslint.config to ESLint core's defineConfig

[bxacosta]

This PR updates the ESLint configuration for the React + TypeScript template, aligning it with the latest typescript-eslint v8.42.0 release, where tseslint.config(...) was deprecated.

Changes

• Migrated the ESLint config from tseslint.config(...) to ESLint core’s defineConfig(...).
• Updated the README to replace usage examples with defineConfig.
• Removed unnecessary spread operator (...) inside extends, since extends can directly accept an array of configurations without spread syntax.

References

• Deprecation of tseslint.config(...): typescript-eslint v8.42.0 release notes
• Migration discussion: typescript-eslint/typescript-eslint#10935
• Migration guide: Migrating to defineConfig
• ESLint docs on extends supporting arrays: Extending Configurations

[sapphi-red]

Thanks!