feat(api): embedding-based semantic clustering with HDBSCAN and auto-labeling

feat(api): add Critical/Important/Low labels to /rank; add /rank_hunks endpoint

chore: exclude large binary files from git, upload via HF Hub API

chore: track binary FAISS files with Git LFS

feat(api): ONNX metrics endpoint, real FAISS retrieval, structured logging

fix(api): normalize reranker logits relatively across PR files

feat(api): load fine-tuned prism-reranker from HF Hub for real ML inference

fix(api): install gcc before user switch to enable hdbscan compilation

feat(api): initial FastAPI deployment for HF Spaces