fix(a11y): ensure Modal always has accessible name via aria-label fallback

[lishmanTech]

Summary

This PR fixes an accessibility issue where the Modal component could be rendered without an accessible name when used without a title prop.

Screen readers previously announced such modals as unnamed dialogs.

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Problem

• Modal.tsx only used aria-labelledby when title was provided
• When title is missing, no fallback aria-label was set
• This resulted in inaccessible dialog announcements for screen readers

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Solution

• Added optional ariaLabel prop to Modal
• When title exists → modal uses aria-labelledby
• When title is missing → modal falls back to aria-label
• Ensures every modal always has an accessible name

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Changes

Modal component

• Added ariaLabel?: string prop
• Added fallback:
  • aria-labelledby if title exists
  • aria-label if title is not provided

Call sites

• Updated title-less modal usage (where applicable) to provide ariaLabel

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Example usage

With title (unchanged)

<Modal
  isOpen={isOpen}
  onClose={onClose}
  title="Dispute Details"
/>

closes #1025