feat: Add Vim Mode and Autocomplete Features to Simple Chat

- Implemented vim-style line editing in the simple chat interface, allowing users to navigate and edit text using familiar vim commands.
- Introduced an autocomplete system in the FTXUI chat, providing real-time command suggestions and fuzzy matching for improved user experience.
- Updated documentation to reflect new features and usage instructions for vim mode and autocomplete functionality.
- Enhanced the TUI with autocomplete UI components for better interaction and command input.

src/cli/service/agent/conversational_agent_service.h

@@ -66,6 +66,7 @@ struct AgentConfig {
   bool show_reasoning = true;    // Show LLM reasoning in output
   size_t max_history_messages = 50;  // Maximum stored history messages per session
   bool trim_history = true;          // Whether to trim history beyond the limit
+  bool enable_vim_mode = false;      // Enable vim-style line editing in simple-chat
   AgentOutputFormat output_format = AgentOutputFormat::kFriendly;
 };