Reactive AI-chat surface: OpenAI-compatible /chat/completions plus the Dify /chat-messages compatibility endpoint, both driven by the same AppGenerateService facade. Built on Spring WebFlux (Netty) so token-level SSE does not tie up a servlet thread per client. Depends on agent-start-web only for the shared ApiResponse envelope; the module itself contains its own SSE bridge, chat DTOs, and workflow/agent generators.