Replace Gemma embedding model with BAAI/bge-small-en-v1.5 and cache at build time

Configure for 100% self-contained CPU deployment

Few tweaks

RAG retreival updates

Restore Phase 5 advanced RAG changes and clean schemas.py

Merge branch 'main' into feature/advanced-rag

Pushing the changes for judge as LLM

initial: RAG Visualizer (Phases 1-4)

local: phase 5 arena and text highlighter