Step 1: Ethernet up (IP101/RMII), DHCP, link and IP logged

- aes67_board: Waveshare ESP32-P4-ETH pin profile and EMAC + IP101 driver
  install (PHY addr 1, reset GPIO51, ref clock in on GPIO50).
- aes67_net: Ethernet netif with DHCP client; logs link up/down (speed,
  duplex, MAC) and the DHCP lease.
- Verified on board: 100 Mbps full duplex, DHCP lease in ~8 s, ping
  0% loss, ~0.2 ms RTT.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main/main.c

@@ -1,3 +1,5 @@
+#include "aes67_board.h"
+#include "aes67_net.h"
 #include "esp_app_desc.h"
 #include "esp_chip_info.h"
 #include "esp_log.h"
@@ -14,4 +16,8 @@ void app_main(void)
              app->project_name, app->version, app->idf_ver, app->date, app->time);
     ESP_LOGI(TAG, "chip rev v%d.%d, %d cores",
              chip.revision / 100, chip.revision % 100, chip.cores);
+
+    esp_eth_handle_t eth;
+    ESP_ERROR_CHECK(aes67_board_eth_init(&eth));
+    ESP_ERROR_CHECK(aes67_net_init(eth));
 }