feat: add priorityAttribute support for element identification

[JungHoe]

Description

This PR addresses an issue where elements were not being optimally identified for testing and automation workflows. It introduces support for a configurable priorityAttribute (defaulting to data-testid), allowing Agentation to generate more robust and reliable selectors.

Changes

• Core Logic: Updated getElementPath, identifyElement, and getFullElementPath utilities to accept and prioritize a priorityAttribute.
• Component: Added priorityAttribute prop to Agentation (default: "data-testid").
• Documentation: Updated API docs and Example app to demonstrate the new feature.
• Example: Added data-testid attributes to demo elements in the example app for immediate verification.

How to Test

1. Run the example app: cd _package-export/example && npm run dev
2. Open http://localhost:3000
3. Click on the "Primary Button" or "Example Card"
4. Verify that the annotation path uses [data-testid="..."] instead of generic classes or tags.

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