Rename the project from "MyLibrary" to "MedicalLib" to better reflect its intended purpose as a library for medical simulations.

- Rename all files, directories, and internal project names to "MedicalLib".
- Replace the generic `add` function with a more domain-specific `calculateBMI` function as an initial example of the library's capabilities.
- Update the `AGENTS.md` file to describe the new purpose and scope of the MedicalLib library.

include/MedicalLib/MedicalLib.h

@@ -0,0 +1,20 @@
+#pragma once
+
+// Define MEDICAL_LIB_EXPORT for exporting symbols from the DLL
+#if defined(_WIN32)
+    #if defined(MEDICAL_LIB_EXPORT)
+        #define MEDICAL_LIB_API __declspec(dllexport)
+    #else
+        #define MEDICAL_LIB_API __declspec(dllimport)
+    #endif
+#else
+    #define MEDICAL_LIB_API
+#endif
+
+/**
+ * @brief Calculates the Body Mass Index (BMI).
+ * @param weight_kg The weight in kilograms.
+ * @param height_m The height in meters.
+ * @return The calculated BMI.
+ */
+MEDICAL_LIB_API double calculateBMI(double weight_kg, double height_m);