feat: redesign backend pdf_generator.py to match premium Clinical Referral Card layout in ReportLab

perf: reduce heatmap from 256 to 16 model inferences + fix gunicorn timeout/workers

fix: collapse python3 -c to single line to fix dockerfile parse error

feat: download ONNX model from HF Hub at build time, add django-cors-headers

deploy: clean initial commit for Hugging Face Spaces (no binary blobs)