feat: Add detailed simulation to remaining simple organs

This commit applies a detailed physiological model to all remaining simple organ classes, bringing them to a level of complexity consistent with the Heart, Lungs, and Brain.

Updates include:
- Esophagus: Simulates peristalsis and bolus movement.
- Stomach: Implements a gastric state machine for digestion.
- Intestines: Adds segments (duodenum, jejunum, etc.) and simulates absorption.
- Pancreas: Differentiates endocrine and exocrine functions.
- Gallbladder: Simulates storing, concentrating, and releasing bile.
- Kidneys: Models nephrons, GFR, and electrolyte balance.
- Bladder: Implements a micturition cycle with pressure dynamics.
- Spleen: Models red and white pulp for blood filtering and immunity.

include/MedicalLib/Gallbladder.h

@@ -1,18 +1,63 @@
 #pragma once
 
 #include "Organ.h"
+#include <string>
 
 /**
- * @brief Represents the Gallbladder.
+ * @brief Represents the contraction state of the gallbladder.
+ */
+enum class GallbladderState {
+    STORING,
+    CONTRACTING
+};
+
+/**
+ * @brief Represents the Gallbladder, which stores and concentrates bile.
  */
 class MEDICAL_LIB_API Gallbladder : public Organ {
 public:
+    /**
+     * @brief Constructor for the Gallbladder class.
+     * @param id The ID of the organ.
+     */
     Gallbladder(int id);
+
+    /**
+     * @brief Updates the gallbladder's state over a time interval.
+     * @param deltaTime_s The time elapsed in seconds.
+     */
     void update(double deltaTime_s) override;
+
+    /**
+     * @brief Gets a string summary of the gallbladder's state.
+     * @return A string containing the gallbladder's state.
+     */
     std::string getSummary() const override;
 
-    double getBileStored() const;
+    /**
+     * @brief Adds bile from the liver.
+     * @param volume_mL The volume of bile to add.
+     */
+    void storeBile(double volume_mL);
+
+    // --- Getters for Gallbladder State ---
+
+    /** @brief Gets the current volume of stored bile in mL. */
+    double getStoredBileVolume() const;
+
+    /** @brief Gets the concentration factor of the stored bile. */
+    double getBileConcentration() const;
+
+    /** @brief Gets the current state of the gallbladder. */
+    GallbladderState getCurrentState() const;
 
 private:
-    double bileStored; // in ml
+    // --- Helper to convert enum to string ---
+    std::string stateToString(GallbladderState state) const;
+
+    // --- Physiological Parameters ---
+    GallbladderState currentState;
+    double storedBile_mL;
+    double bileConcentrationFactor; // How concentrated the bile is (1x, 5x, etc.)
+    const double capacity_mL = 50.0;
 };