fix: Gradio 6.0 compatibility — move css to launch(), remove Chatbot type arg

feat: model selector, progress bar, sources panel, chat export, CSV parsing, dockerignore

fix: remove gradio pin + drop type='messages' for HF Spaces 6.6.0 compat

fix: model singleton cache, dedup guard, Gradio type=messages

feat: apply all 15 upgrades — BGE embeddings, cosine FAISS, streaming LLM, tenacity retry, dotenv, Dockerfile, tests

Add Kerdos Infrasoft branding, demo banner, and funding CTA

Fix Gradio 6.x compatibility errors