Add ESP-NOW master/slave discovery on DIP network channel.

Initialize WiFi and ESP-NOW from shared app config; master broadcasts
discover packets and collects slave info, slaves respond on matching
network while UART commands stay master-only.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/app_config.h

@@ -0,0 +1,15 @@
+#ifndef APP_CONFIG_H
+#define APP_CONFIG_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#define APP_RUNNING_PARTITION_LABEL_MAX 17
+
+typedef struct {
+  bool master;
+  uint8_t network;
+  char running_partition[APP_RUNNING_PARTITION_LABEL_MAX];
+} app_config_t;
+
+#endif