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>

components/aes67_board/include/boards/waveshare_esp32p4_eth.h

@@ -0,0 +1,17 @@
+// Waveshare ESP32-P4-ETH (PoE): pin profile.
+// IP101GRI PHY over RMII, 50 MHz ref clock from the PHY into the EMAC.
+#pragma once
+
+#define BOARD_NAME          "Waveshare ESP32-P4-ETH"
+
+#define BOARD_ETH_PHY_ADDR  1
+#define BOARD_ETH_PHY_RST   51      // PHY reset/power
+#define BOARD_ETH_MDC       31
+#define BOARD_ETH_MDIO      52
+#define BOARD_ETH_REF_CLK   50      // EMAC_CLK_EXT_IN
+#define BOARD_ETH_TX_EN     49
+#define BOARD_ETH_TXD0      34
+#define BOARD_ETH_TXD1      35
+#define BOARD_ETH_CRS_DV    28
+#define BOARD_ETH_RXD0      29
+#define BOARD_ETH_RXD1      30