Add parameterized ShapeContractTest for Shape interface invariants

Verify clone(), getBounds(), and translate() contracts across all Shape
implementations (SRectangle, SCircle, STriangle, SText, SCollection)
using @ParameterizedTest + @MethodSource.

Also adds junit-jupiter-params dependency to pom.xml.

Closes #8

src/test/java/ovh/gasser/newshapes/shapes/ShapeFactory.java

@@ -0,0 +1,25 @@
+package ovh.gasser.newshapes.shapes;
+
+import java.awt.Color;
+import java.util.stream.Stream;
+
+/**
+ * Provides Shape instances for parameterized contract tests.
+ */
+public final class ShapeFactory {
+
+    private ShapeFactory() {}
+
+    static Stream<Shape> allShapes() {
+        return Stream.of(
+                SRectangle.create(10, 20, 100, 50),
+                SCircle.create(5, 5, 30),
+                STriangle.create(0, 0, 40, Color.RED, Color.BLACK),
+                SText.create(15, 25, "Hello"),
+                SCollection.of(
+                        SRectangle.create(0, 0, 20, 20),
+                        SCircle.create(10, 10, 5)
+                )
+        );
+    }
+}