[feat] 100Hz task switch

include/scheduler.h

@@ -7,6 +7,7 @@
 #define TASK_STACK_SIZE  (PAGE_SIZE * 4)  // 16 KB kernel stack per task
 #define TASK_MAX         32
 #define TASK_NAME_LEN    32
+#define TIME_SLICE_DEFAULT 5  // 5 ticks = 50ms at 100 Hz
 
 typedef enum {
     TASK_STATE_READY,
@@ -21,6 +22,7 @@ typedef struct task {
     char            name[TASK_NAME_LEN];
     void*           stack_base;     // base address of kernel stack
     struct task*    next;           // circular linked list
+    UINT32          time_slice;     // remaining ticks before preemption
 } task_t;
 
 // Create a new task. Returns task pointer or NULL on failure.
@@ -37,3 +39,6 @@ void task_exit(void);
 
 // Get current running task
 task_t* scheduler_current(void);
+
+// Timer tick handler — called by PIT IRQ 0, drives preemption
+void scheduler_tick(void);