Implemented Next.js API route at /api/chat with:
- POST endpoint for sending messages with streaming responses (SSE)
- GET endpoint for retrieving chat history
- OPTIONS endpoint for CORS preflight
- Integration with Deepseek API via createStreamingChatCompletion
- Session management via getOrCreateChatSession (24h continuity)
- Message persistence to Supabase (user + assistant messages)
- Context management with 20-message history limit
- Error handling for API key/database issues
- Request validation for required fields (message, visitorId)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
