feat: add abstract Vehicle base class

src/main/java/org/example/model/Vehicle.java

@@ -0,0 +1,38 @@
+package org.example.model;
+
+/*
+ * Abstract base class for all vehicles.
+ * This class DOES NOT implement Serviceable.
+ * Service behavior will be defined in concrete subclasses.
+ */
+
+public abstract class Vehicle {
+
+    private String brand;
+    private String model;
+    private int year;
+    private double mileage;
+
+    public Vehicle(String brand, String model, int year, double mileage) {
+        this.brand = brand;
+        this.model = model;
+        this.year = year;
+        this.mileage = mileage;
+    }
+
+    // TODO: Create getters for all fields
+
+    // TODO: Implement addMileage(double km)
+    // If km is negative → print error
+    // Otherwise increase mileage
+
+    // TODO: Declare abstract method getEnergyType()
+
+    public void basicInfo() {
+        System.out.println(
+                year + " " + brand + " " + model +
+                        " | Mileage: " + mileage +
+                        " | Energy: " + getEnergyType()
+        );
+    }
+}