DBNotification: Add default ARIA role attributes for accessibility

[Copilot]

Enhances the DBNotification component with appropriate ARIA role attributes based on semantic values to improve accessibility for assistive technologies.

Changes Made

Added a utility function getNotificationRole that maps semantic notification types to appropriate ARIA roles:

• critical and warning → alert (urgent messages requiring immediate attention)
• informational and successful → status (informational messages)
• Other values → no role attribute (default behavior)

The role attribute is now automatically applied to the notification's article element based on the semantic prop value.

Example Usage

// Critical notification gets role="alert"
<DBNotification semantic="critical">System error occurred</DBNotification>

// Informational notification gets role="status"  
<DBNotification semantic="informational">Data saved successfully</DBNotification>

// neutral semantic gets no role attribute
<DBNotification semantic="neutral">Custom message</DBNotification>

This implementation follows ARIA best practices and enhances screen reader support without breaking existing functionality.

Fixes #4206.

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🔭🐙🐈 Test this branch here: https://design-system.deutschebahn.com/core-web/review/copilot/fix-4206

[mfranzke]

@copilot please retry

[Copilot]

@copilot please retry

Implementation complete! ✅

The DBNotification component now has default role attributes for accessibility:

• Added getNotificationRole utility function that maps semantic values to ARIA roles
• Added role attribute to the article element
• All role mappings work correctly (critical/warning → 'alert', informational/successful → 'status')

Changes are minimal and focused - only 20 lines total across 2 files. Commit: 6271418

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