feat: add asset preferences, video research, and Remotion ad assets

- Add thumbs-down feedback modal and preference API endpoint
- Add AI UGC video platforms research doc
- Add ReflectAd Remotion composition with public flow assets
- Add gemini-ad-designer and poster-ad-designer pipeline skills
- Add research_reflect_v1.1 pipeline script

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

prisma/schema.prisma

@@ -27,6 +27,7 @@ model App {
   brandIdentity      String?
   productInfo        String?
   platformGuidelines String?
+  stylePreferences   String?    // JSON: { liked: [...], disliked: [...] }
   createdAt          DateTime   @default(now())
   updatedAt          DateTime   @updatedAt
   campaigns          Campaign[]