Implement streaming responses for chat interface

Description

Implement server-sent events (SSE) for streaming AI responses in real-time instead of waiting for complete response.

Benefits

• Better UX with instant feedback
• Reduced perceived latency
• Ability to stop generation mid-stream

Tasks

• Add EventSource API implementation
• Create streaming response UI component
• Add loading states and animations
• Implement cancellation tokens
• Add error handling for connection drops
• Write integration tests

cc @michael @stan