feat: replace mocktail placeholders with real Unsplash photos + add screenshots

Real cocktail photos from Unsplash (free license) for all 10
non-alcoholic cocktails. Also adds iOS and Android screenshots
for documentation.

Photo credits (Unsplash):
- Virgin Mojito: ABHISHEK HAJARE
- Shirley Temple: (strawberry cocktail)
- Virgin Piña Colada: YesMore Content
- Roy Rogers: (cola glass)
- Arnold Palmer: Misunderstood Whiskey
- Virgin Mary: Toni Osmundson
- Nojito: Yubraj Timsina
- Cinderella: (orange juice)
- Safe Sex on the Beach: (peach cocktail)
- Italian Soda: (cream soda)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kherembourg