- Remove unused context_build_messages() (superseded by direct cJSON in agent_loop)
- Remove unused llm_chat() and its helper extract_text_* functions (superseded by llm_chat_tools)
- Remove ota_manager.c from build (never called)
- Remove config_screen.c stub from build (no-op module)
- Remove unused PWR_KEY_State, Button_GPIO_Get_Level; drop config_screen dependency from button_driver
- Fix incorrect type cast in tool_get_time.c (char[64] cast to char**)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
