Create SQL migration for chatbot database tables:
- chat_sessions: Stores visitor session data with visitor_id, metadata, timestamps
- chat_messages: Stores chat messages with role (user/assistant/system), content
- Proper indexes for visitor lookup and message ordering
- Row Level Security (RLS) enabled with policies for:
- Service role full access (for server-side API)
- Visitor-based access via x-visitor-id header (for potential future client-side)
- Trigger for automatic updated_at column on chat_sessions
Also updated ChatSession interface in chat.ts to include updated_at field.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>