feat: add eslint-plugin-jsx-a11y via jsx.a11y option

[ccpu]

Description

This PR adds support for JSX accessibility (a11y) rules using the eslint-plugin-jsx-a11y.
it can be enable as follow:

jsx: {
  a11y: true
}

or customize with overrides:

jsx: {
  a11y: {
    overrides: { /* custom a11y rules */ }
  }
}

I chose to integrate a11y as a sub-option of the jsx prop for a unified, DRY, and extensible API mirroring the approach used for Vue a11y. This keeps all JSX related config in one place and makes future extension easier.

Additional context

• eslint-plugin-jsx-a11y is widely adopted and considered an industry standard, so having it included in this library would be nice.
• I have added a separate test to ensure a11y rules are applied correctly.
• Please check the new config structure and let me know if further tweaks are needed.

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