fix: add dummy dispatch function and update engine_init call in test_gui.c

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

test_gui.c

@@ -3,12 +3,16 @@
 #include "engine.h"
 #include "gui.h"
 
+static void dummy_dispatch(Action action) {
+    (void)action;
+}
+
 int main(void)
 {
     Engine engine;
     const char *client_name = "jack_looper_gui_test";
 
-    if (engine_init(&engine, client_name) != 0) {
+    if (engine_init(&engine, client_name, dummy_dispatch) != 0) {
         fprintf(stderr, "Failed to initialize engine\n");
         return 1;
     }