Add web search fallback for Video Brain when YouTube transcript fails due to network issues

Add YouTube transcript extraction, improve Video Brain with follow-up questions, fix all modes

Fix model, improve error handling, add startup diagnostics for all modes

Major fix: Improved web search with Tavily AI answers, better content extraction, enhanced system prompt

Fix all modes - use WebSearchGraph, fix image format, add trafilatura

Fix: Tavily API format and Streamlit image compatibility

Add Product MVP and Video Brain modes + Render deployment

Fix: LangChain 0.2.x compatibility - update imports and model config

Fix: Lightweight requirements for Azure - CPU-only PyTorch

Perplexity AI Clone - Full Production Version with 8 Modes