docs(toast): document useToast API, quiet mode, and announcers

[akprinciple]

closes #380

This PR introduces comprehensive documentation for the ToastProvider system and strengthens its test coverage to align with the documented behavior. The toast provider is a critical, user-facing component, and this work provides a durable reference for its API and features.

Key Changes

• New Documentation (docs/components/Toast.md): Created a complete reference document covering:
  • The ToastProvider and useToast hook API.
  • Behavioral guarantees for features like Quiet Mode, auto-dismiss duration, density, and toast eviction.
  • Detailed accessibility implementation, including role attributes and the ToastAnnouncer live regions.
• JSDoc Enhancements: Added detailed JSDoc comments to src/components/toast/toast-provider.tsx, linking directly to the new documentation and summarizing key behaviors in-code.
• Test Suite Improvements: Added new test cases to toast-provider.test.tsx to explicitly verify behaviors mentioned in the documentation, such as aria-atomic attributes and eviction logic.

This resolves the issue of scattered or missing documentation for a central UI component, making it easier for developers to use the toast system correctly and safely.

[mikewheeleer]

good stuff here — merged with thanks 🚀