feat(react): implement reusable and accessible modal component (#227)

[iamTissan]

What does this PR do?

Introduces a modular, fully accessible (a11y), and responsive native React Modal component inside the @bc-forge/react library package.

Key implementation details include:

• Accessibility Foundations: Built using native ARIA attributes (role="dialog", aria-modal="true", aria-labelledby) conforming to WCAG standards.
• Keyboard Navigation: Implements an active keyboard focus trap using custom vanilla React hooks to lock focus context sequentially within active modal elements, alongside native Escape key dismissal support.
• Design Tokens: Configured with robust structure variants (sm, md, lg) and responsive tailwind frame wrapping layout support, including context borders for variant states (e.g., danger).
• State Cleanup: Auto-restores the previously focused element upon unmounting and isolates underlying frame scrolling via body locking configurations.
• Test Coverage: Added comprehensive test suites verifying conditional viewport rendering, backdrop wrapper event bubbling/isolation, escape trigger captures, and custom child focus constraints.

Type of change

• Bug fix
• Feature
• Refactor
• Docs
• CI
• Chore

Checklist

• I ran pre-commit run --all-files locally and it passed
• All CI jobs pass on this branch
• I added or updated tests for new behaviour
• I updated relevant docs / comments
• No secrets or credentials are included
• No breaking changes to public APIs (or I've documented them)

Breaking changes?

No.

Related issues

Closes #227

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