feat: Ultrafast preset for all modules, Text Story margin fix, Quiz Explain box improvements

Add heading with background support: centered layout, heading BG, fact text outline/shadow

Pexels: select FIRST most relevant photo instead of random

Simplify image prompt: remove confusing keywords, clear NO TEXT instruction

Fix HF storage: correct import (get_hf_storage) and upload_video args

Fix fact_creator: correct API signatures (NVIDIA/CF/Pexels), ensure 9:16 video output

Add Fact-Image module: generate videos with fact text overlay on AI images