Sync Gemini key/error fixes and deployment notes from main

Update README.md

Add Gemini key guard and update README

Show sample query on user side using type="user_message"

Fix sample query user message not shown and double-processing

Fix double-processing on sample query and quick reply actions

Fix examples and Gemini welcome; add filtered_queries.json

Mount Chainlit at root path for HF Spaces iframe compatibility

Initial deployment: Sustainable Tourism CRS Chatbot