Rewrite ConversationManager component with simplified state management

- Fixed property access issues in JSX rendering
- Simplified data structure using single ConversationData interface
- Corrected SDK API usage (host instead of baseUrl, getAllConversations instead of listConversations)
- Fixed agent status access through state.getAgentStatus()
- Removed complex state mixing between ConversationInfo and RemoteConversation types
- Improved error handling and loading states
- Added proper TypeScript types for all data structures
- Cleaned up component structure for better maintainability

This resolves the conversation details display issue where data was available
but JSX rendering showed blank values due to incorrect property access.

Author: openhands-agent