Deploy: Update for Hugging Face (Secrets + Port) and Vercel Proxy

fix(security): remove hardcoded HF_API_KEY from main.py

chore(env): rotate HF token and restore Pinecone API key

feat(search): apply year range post-filter and expose filtered count

perf(search): increase Pinecone fetch pool when year filter is active

fix(security): replace Pinecone API key with env var

feat(models): extend SearchRequest with optional year_from and year_to fields

feat(backend): initialize FastAPI app