feat: ICMP ping test, IOAPIC level-triggered PCI IRQ, multi-disk test battery

feat: ICMP ping test, IOAPIC level-triggered PCI IRQ, multi-disk test battery

- net_ping.c: kernel ICMP ping test using lwIP raw API with inline
  e1000_recv polling (3 pings to 10.0.2.2 QEMU gateway)
- ioapic: add ioapic_route_irq_level() for PCI interrupts
  (level-triggered, active-low per PCI spec)
- arch_platform: route E1000 NIC IRQ 11 via ioapic_route_irq_level
- e1000_netif: rx_thread uses process_sleep(1) polling fallback
- smoke_test.exp: add PING network pattern (20/20 tests)
- test_battery.exp: 16 tests covering multi-disk ATA detection
  (hda+hdb+hdd), VFS InitRD+diskfs mount, ping, and diskfs ops
- Makefile: add test-battery target and -nic user,model=e1000