Generate app store listing materials (screenshots, descriptions, icons)

[JesseRWeigel]

Create all materials needed for Google Play, Apple App Store, and Amazon Appstore submissions.

Need:

• App icon (512x512 PNG and 1024x1024)
• Feature graphic (1024x500 for Google Play)
• 4-6 screenshots at phone resolution (1080x1920) and tablet (1200x1920)
• Short description (80 chars)
• Full description (4000 chars)
• Keywords
• Category selection (Education > Math)
• Age rating questionnaire answers
• Privacy policy URL

Can generate icon with FLUX.1 and take screenshots with Playwright.

Acceptance criteria:

• All assets in a release/store-assets/ directory