Test: Try cooperative scheduling for mutex test

Diagnostic output revealed printf hangs after printing only '[' character
before enabling preemptive scheduling. This suggests either:
1. Printf buffer/UART issue when transitioning to preemptive mode
2. Preemptive scheduler itself has initialization issues

Changes:
- Removed diagnostic printfs that cause hangs
- Changed return true → false to test with cooperative scheduling
- Added '(cooperative mode)' to output for visibility

If cooperative mode works, the issue is in preemptive scheduler initialization.
If it still hangs, the problem is elsewhere (semaphore/task logic).

Author: jserv

app/mutex.c

@@ -18,7 +18,7 @@ static int currently_in_critical_section = 0;
 /* Enhanced Task A */
 void task_a(void)
 {
-    printf("[DIAG] Task A entry point reached\n");
+    /* WORKAROUND: Printf may hang - skip diagnostic */
     printf("Task A (ID %d) starting...\n", mo_task_id());
 
     for (int i = 0; i < MAX_ITERATIONS; i++) {
@@ -71,7 +71,7 @@ void task_a(void)
 /* Enhanced Task B */
 void task_b(void)
 {
-    printf("[DIAG] Task B entry point reached\n");
+    /* WORKAROUND: Printf may hang - skip diagnostic */
     printf("Task B (ID %d) starting...\n", mo_task_id());
 
     for (int i = 0; i < MAX_ITERATIONS; i++) {
@@ -132,7 +132,7 @@ void task_b(void)
 /* Simple monitor task */
 void monitor_task(void)
 {
-    printf("[DIAG] Monitor entry point reached\n");
+    /* WORKAROUND: Printf may hang - skip diagnostic */
     printf("Monitor starting...\n");
 
     int cycles = 0;
@@ -222,7 +222,6 @@ int32_t app_main(void)
     printf("Tasks created: A=%d, B=%d, Monitor=%d, Idle=%d\n", (int) task_a_id,
            (int) task_b_id, (int) monitor_id, (int) idle_id);
 
-    printf("Starting test...\n");
-    printf("[DIAG] About to enable preemptive scheduling\n");
-    return true; /* Enable preemptive scheduling */
+    printf("Starting test (cooperative mode)...\n");
+    return false; /* TEST: Try cooperative scheduling first */
 }