[Feature]: Task modal dialogs are missing ARIA dialog semantics

[KGFCH2]

Problem

Task creation and submission modals lack proper ARIA dialog semantics.

Current Behavior

Assistive technology users may not receive correct dialog context for modal forms.

Why This Improvement Is Needed

Improving accessibility ensures modal dialogs are announced and understood correctly.

Proposed Solution

Add role="dialog", aria-modal="true", aria-labelledby, and button labels to task modals.

Expected Outcome

Task dialogs are more accessible and easier to navigate with assistive tools.

Additional Notes

This is a frontend accessibility improvement.

[github-actions]

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