Remove first-task binding from task initialization

Previously, both mo_task_spawn() and idle_task_init() implicitly
bound their created tasks to kcb->task_current as the first execution
context. This behavior caused ambiguity with the scheduler, which is
now responsible for determining the active task during system startup.

This change removes the initial binding logic from both functions,
allowing the startup process (main()) to explicitly assign
kcb->task_current (typically to the idle task) during launch.
This ensures a single, centralized initialization flow and improves
the separation between task creation and scheduling control.

Author: vicLin8712

kernel/task.c

@@ -721,9 +721,6 @@ void idle_task_init(void)
     printf("idle id %u: entry=%p stack=%p size=%u\n", idle->id, &sched_idle,
            idle->stack, (unsigned int) stack_size);
 
-    if (!kcb->task_current)
-        kcb->task_current = kcb->harts->task_idle;
-
     return;
 }
 
@@ -789,10 +786,6 @@ int32_t mo_task_spawn(void *task_entry, uint16_t stack_size_req)
 
     /* Push node to ready queue */
     sched_enqueue_task(tcb);
-    if (!kcb->task_current) {
-        kcb->task_current = kcb->harts->rr_cursors[tcb->prio_level];
-        tcb->state = TASK_RUNNING;
-    }
 
     CRITICAL_LEAVE();