[Agent] Implement real-time chat system for human-agent collaboration

[coderabbitai]

Overview

Build the chat interface and backend for collaborating with AI agents.

Current State

• Complete type definitions (ChatThread, ChatMessage, MessageContent)
• No implementation exists
• No chat UI components

Requirements

• Create src/services/chat/ directory
• Implement ChatService:
  • Thread management (create, list, delete)
  • Message sending/receiving
  • Streaming message support
  • Multi-modal content (text, code, files, actions)
  • Context management
• Build chat UI components:
  • ChatBubble (user/agent messages)
  • CodeBlock with syntax highlighting
  • FileDiff viewer
  • ActionButtons (approve/reject)
  • TypingIndicator
• Add real-time updates
• Implement message persistence
• Add search functionality
• Support file attachments
• Write tests and documentation

Success Criteria

• Smooth real-time chat experience
• Code diffs rendered beautifully
• All message types supported
• Offline message queue

Priority: HIGH

Estimated Effort: 6-8 days

Dependencies: State Management, Agent System

Labels: agent, chat, ui, priority:high

Backlink: Related to PR #2