Add 0x0026a custom AES-128-CMAC secure bootloader, Week 11a notebook, and README links

0x0026a_custom-bootloader/common/include/mbedtls_config.h

@@ -0,0 +1,25 @@
+/**
+ * @file mbedtls_config.h
+ * @brief Minimal Mbed TLS configuration for the 0x0026a bootloader and app.
+ * @author Kevin Thomas
+ * @date 2026
+ *
+ * MIT License
+ * Copyright (c) 2026 Kevin Thomas
+ *
+ * The Pico SDK points MBEDTLS_CONFIG_FILE at pico_mbedtls_config.h, which in
+ * turn includes this file. Only the AES-128 building blocks needed for CMAC
+ * authentication and CBC encryption are enabled, keeping the image small.
+ */
+
+#ifndef MBEDTLS_CONFIG_H
+#define MBEDTLS_CONFIG_H
+
+#include <limits.h>
+
+#define MBEDTLS_AES_C
+#define MBEDTLS_CIPHER_C
+#define MBEDTLS_CIPHER_MODE_CBC
+#define MBEDTLS_CMAC_C
+
+#endif