Refactor sched_enqueue_task() for O(1) scheduler support

Previously, sched_enqueue_task() only changed task state without inserting
into ready queue. As a result, the scheduler could not select enqueued task
for execution.

This change pushes the task into the appropriate ready queue using
list_pusback(), and initializes realated attribution such as the
ready bitmap and RR cursor. The ready queue for corresponging task
priority will be initialized at this enqueue path and never be
released afterward.

With this updated API, tasks can be enqueued into the ready queue and
selected by cursor-based O(1) scheduler.

Author: vicLin8712

kernel/task.c

@@ -82,7 +82,7 @@ static const uint8_t priority_timeslices[TASK_PRIORITY_LEVELS] = {
     TASK_TIMESLICE_IDLE      /* Priority 7: Idle */
 };
 
-/* Mark task as ready (state-based) */
+/* Enqueue task into ready queue */
 static void sched_enqueue_task(tcb_t *task);
 
 /* Utility and Validation Functions */
@@ -349,17 +349,41 @@ void _yield(void) __attribute__((weak, alias("yield")));
  * practical performance with strong guarantees for fairness and reliability.
  */
 
-/* Add task to ready state - simple state-based approach */
+/* Enqueue task into ready queue */
 static void sched_enqueue_task(tcb_t *task)
 {
     if (unlikely(!task))
         return;
 
+    uint8_t prio_level = task->prio_level;
+
     /* Ensure task has appropriate time slice for its priority */
-    task->time_slice = get_priority_timeslice(task->prio_level);
+    task->time_slice = get_priority_timeslice(prio_level);
     task->state = TASK_READY;
 
-    /* Task selection is handled directly through the master task list */
+    list_t **rq = &kcb->harts->ready_queues[prio_level];
+    list_node_t **cursor = &kcb->harts->rr_cursors[prio_level];
+
+    if (!*rq)
+        *rq = list_create();
+
+    list_node_t *rq_node = list_pushback(*rq, task);
+    if (unlikely(!rq_node))
+        return;
+
+    /* Update task count in ready queue */
+    kcb->harts->queue_counts[prio_level]++;
+
+    /* Setup first rr_cursor */
+    if (!*cursor)
+        *cursor = rq_node;
+
+    /* Advance cursor when cursor same as running task */
+    if (*cursor == kcb->task_current)
+        *cursor = rq_node;
+
+    BITMAP_SET(task->prio_level);
+    return;
 }
 
 /* Remove task from ready queues - state-based approach for compatibility */