Add data structures for O(1) scheduler

This commit extends the core scheduler data structures to support
the new O(1) scheduler design.

Adds in tcb_t:

 - rq_node: embedded list node for ready-queue membership used
   during task state transitions. This avoids redundant malloc/free
   for per-enqueue/dequeue nodes by tying the node's lifetime to
   the task control block.

Adds in kcb_t:

 - ready_bitmap: 8-bit bitmap tracking which priority levels have
   runnable tasks.
 - ready_queues[]: per-priority ready queues for O(1) task
   selection.
 - rr_cursors[]: round-robin cursor per priority level to support
   fair selection within the same priority.

These additions are structural only and prepare the scheduler for
O(1) ready-queue operations; they do not change behavior yet.

Author: vicLin8712

include/sys/task.h

@@ -86,6 +86,10 @@ typedef struct tcb {
 
     /* Stack Protection */
     uint32_t canary; /* Random stack canary for overflow detection */
+
+    /* State transition support */
+    /* Ready queue membership node (only one per task) */
+    list_node_t rq_node;
 } tcb_t;
 
 /* Kernel Control Block (KCB)
@@ -108,6 +112,12 @@ typedef struct {
     /* Timer Management */
     list_t *timer_list;      /* List of active software timers */
     volatile uint32_t ticks; /* Global system tick, incremented by timer */
+
+    /* Scheduling attributions */
+    uint8_t ready_bitmap; /* 8-bit priority bitmap */
+    list_t
+        *ready_queues[TASK_PRIORITY_LEVELS]; /* Separate queue per priority */
+    list_node_t *rr_cursors[TASK_PRIORITY_LEVELS]; /* Round-robin position */
 } kcb_t;
 
 /* Global pointer to the singleton Kernel Control Block */

kernel/task.c

@@ -26,6 +26,9 @@ static kcb_t kernel_state = {
     .task_count = 0,
     .ticks = 0,
     .preemptive = true, /* Default to preemptive mode */
+    .ready_bitmap = 0,
+    .ready_queues = {NULL},
+    .rr_cursors = {NULL},
 };
 kcb_t *kcb = &kernel_state;