feat: latest videos endpoint returns newest 3 #9
Description
Goal\n----\nReturn the 3 most recently uploaded videos for GET /api/v1/videos/latest.\n\nAcceptance criteria\n--------------------\n1. Endpoint returns up to 3 newest videos sorted by added_date descending.\n2. Implementation queries primary videos table (no day partition filter).\n3. Home page row renders these 3 videos.\n4. Unit tests updated and pass.\n\nContext: Chat conversation on 2025-07-08.