feat: define reviewed Academy media assets

[botsarefuture]

Purpose

Begin Milestone 6 with a versioned, accessible educational-media contract proven against real Foundations media.

Changes

• Validate media identity, locale, source, rights, accessibility, and review metadata.
• Require alt text for images, transcripts for audio/video, and captions for video.
• Validate the existing voice-pathway illustration as the first real fixture.
• Document replacement and localization principles.

Checks

• npm tests and build
• Python server tests
• Python compilation
• version and diff checks