feat: add microui-based GUI with transport controls and progress bar

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

test_gui.c

@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <jack/jack.h>
+#include "engine.h"
+#include "gui.h"
+
+static jack_client_t *client = NULL;
+static float *buffer = NULL;
+static int buffer_size = 0;
+
+int main(void)
+{
+    /* create JACK client */
+    const char *client_name = "jack_looper_gui_test";
+    jack_options_t options = JackNullOption;
+    jack_status_t status;
+
+    client = jack_client_open(client_name, options, &status);
+    if (client == NULL) {
+        fprintf(stderr, "jack_client_open() failed, status = 0x%2.0x\n", status);
+        if (status & JackServerFailed) {
+            fprintf(stderr, "Unable to connect to JACK server\n");
+        }
+        return 1;
+    }
+
+    /* allocate audio buffer */
+    buffer_size = 4096;
+    buffer = calloc(buffer_size, sizeof(float));
+    if (!buffer) {
+        fprintf(stderr, "Failed to allocate audio buffer\n");
+        jack_client_close(client);
+        return 1;
+    }
+
+    /* initialize engine */
+    if (engine_init(client, buffer, buffer_size) != 0) {
+        fprintf(stderr, "Failed to initialize engine\n");
+        free(buffer);
+        jack_client_close(client);
+        return 1;
+    }
+
+    /* run GUI */
+    int ret = gui_main(client, buffer, buffer_size);
+
+    /* cleanup */
+    engine_cleanup(client);
+    free(buffer);
+    jack_client_close(client);
+
+    return ret;
+}