fix: answer key timeout, frontend error handling, SonarLint issues

fix: resolve HuggingFace deployment issues (video API, sanitization, prompt engineering, section detection)

chore: trigger HF rebuild

fix: add gcc+python3-dev for pycairo build; move UV_TORCH_BACKEND before uv sync to prevent CUDA downloads

feat: Manim animated video (code write-on, flowcharts, concept cards); slideshow fallback; fix video None model; cache TTS engine; strip emoji from PDF; Manim+ffmpeg system deps in Dockerfile

fix: video None model + slideshow fallback (Pillow+ffmpeg); cache TTS engine; strip emoji from PDF filenames; pin setuptools<81; pass audio to video

feat: full Docker extras (pdf+tts+video); frontend audio/video controls; updated docs and meta tags

fix: Dockerfile installs pdf extra; test_web.py uses pytest fixture for isolation

Add Apache 2.0 license, HF Spaces config, configurable port

feat(deps): replace WeasyPrint with Playwright for PDF generation

feat: add EPUB support and redesign web UI

feat: Docker containerization, packaging, and README overhaul