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

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

fix: sentence-aware chunking, score threshold, DOCX tables, streaming error handling, LLM_MODEL env var

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