fix Hugging Face README YAML metadata

ci: raise coverage gate from 70% to 80%, ignore load tests in pytest, add badges to README

docs: fix stale architecture doc, add README badges, CONTRIBUTING, PR template

docs(readme): add HF Spaces metadata header and setup instructions

docs: remove LangChain from tech stack (not used); document actual OpenRouter/httpx stack

fix: add HF Spaces metadata and fix Dockerfile entrypoint

docs: add README, architecture docs, api docs and basic tests