debug(timer): timer_init 读 PIT 计数器，验证 PIT 是否在走

中断仍不送达 timer_handler（无 H）。读 PIT 计数器（latch+读 0x40）打印：
- 计数在 1~1193 之间变化 → PIT 正常，问题在中断送达（PIC/APIC/IDT）
- 计数为 0/不变 → PIT 本身没跑（outb 未生效/环境问题）
用后移除。

VKernel/Kernel/platform/pch/timer.vp

@@ -3,6 +3,7 @@ import platform.pch.pit as pit
 import sched.sched as sched
 import drivers.core.cpu.apic as apic
 import drivers.serial.uart.serial as serial
+import viperlib
 import asm
 import t, c
 
@@ -25,6 +26,14 @@ def timer_init():
     timer_running = True
     c.Asm("mfence", op=[t.ASM_DESCR.CLOBBER_MEMORY])
     pit.pit_init(TIMER_FREQUENCY)
+    # [DBG] 读 PIT 计数器验证是否在走（用后移除）
+    asm.outb(0x43, 0x00)  # latch channel 0
+    _lo: t.CUInt8T = asm.inb(0x40)
+    _hi: t.CUInt8T = asm.inb(0x40)
+    _cnt: t.CInt = t.CInt(_lo) | (t.CInt(_hi) << 8)
+    _cb: t.CArray[t.CChar, 40]
+    viperlib.snprintf(c.Addr(_cb), 40, "[PIT] cnt=%d\n", _cnt)
+    serial.puts(c.Addr(_cb))
 
 def timer_handler():
     global ticks, seconds, milliseconds, timer_running, _dbg_once