test(network): added DNS resolution verification and extended test script

- Updated init.nim with post-fix DNS resolution test (google.com).
- Added test_network_extended.sh with 120s timeout to allow full DHCP/DNS cycle.
- Validates the fix for the UDP PCB pool exhaustion crash.

apps/init/init.nim

@@ -78,6 +78,32 @@ proc main() =
   print(cstring("[TEST]   - ICMP Echo Request (10.0.2.15 -> 10.0.2.2)\n"))
   print(cstring("[TEST]   - ICMP Echo Reply (10.0.2.2 -> 10.0.2.15)\n\n"))
 
+  # --- DNS RESOLUTION TEST ---
+  print(cstring("\n[TEST] ══════════════════════════════════════\n"))
+  print(cstring("[TEST] DNS Resolution Test\n"))
+  print(cstring("[TEST] Target: google.com\n"))
+  print(cstring("[TEST] ══════════════════════════════════════\n\n"))
+  
+  var dns_success = false
+  for attempt in 1..3:
+    print(cstring("[TEST] DNS Attempt... "))
+    
+    if getaddrinfo("google.com", nil, nil, addr res) == 0:
+      print(cstring("SUCCESS!\n"))
+      dns_success = true
+      freeaddrinfo(res)
+      break
+    else:
+      print(cstring("FAILED. Retrying in 2s...\n"))
+      for j in 1..20:
+        pump_membrane_stack()
+        discard syscall(0x65, 100000000'u64)
+  
+  if dns_success:
+    print(cstring("[TEST] ✓ DNS: PASS\n\n"))
+  else:
+    print(cstring("[TEST] ✗ DNS: FAIL\n\n"))
+
   # Spawn mksh as a separate fiber fibers (NOT execv - we stay alive as supervisor)
   proc spawn_fiber(path: cstring): int =
     # SYS_SPAWN_FIBER = 0x300