artifact: apps/server/src/main/kotlin/com/correx/apps/server/ws/SessionStreamHandler.kt
purpose: Add a when branch for ClientMessage.ChatInput in handleClientMessage() that dispatches to module.routerFacade and sends RouterResponseMessage back over WebSocket.
depends_on: task-014, task-015
non_goals: Creating RouterFacade, adding new protocol types, modifying infrastructure wiring
done_when: Chat and steering messages route to RouterFacade correctly and responses are sent back over WebSocket
