Add checklists and Media tutorials

[alexislucio]

Adds engineering and design checklist from Figma, and adds Media (video, audio, and image) to tutorials folder.

[Copilot]

Pull Request Overview

This PR introduces comprehensive accessibility documentation and checklists for the annotation toolkit. The purpose is to provide practical guidance for implementing accessible media elements and comprehensive accessibility checklists for design and engineering teams.

• Adds a complete media accessibility tutorial covering images, video, and audio with annotation guidance
• Introduces engineering and designer checklists for WCAG 2.2 compliance
• Provides detailed implementation guidance with tools, resources, and exercises for each accessibility category

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
tutorials/media.md	Comprehensive tutorial on accessible media implementation with annotation examples and best practices
checklists/engineering-checklist.md	WCAG 2.2 compliance checklist organized by engineering concerns with tools and resources
checklists/designer-checklist.md	WCAG 2.2 compliance checklist organized by design considerations with annotation guidance

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