fix: SText.updateMeasuredBounds() must mutate internal bounds, not defensive copy

Closes #27

TODO.md

@@ -1,6 +1,6 @@
 # TODO
 
-- [ ] Box selection (drag to select multiple shapes)
+- [X] Box selection (drag to select multiple shapes)
 - [ ] Undo/redo stack
 - [ ] Copy/paste functionality
 - [ ] Group/Ungroup shapes

src/main/java/ovh/gasser/newshapes/shapes/SText.java

@@ -57,7 +57,7 @@ public class SText extends AbstractShape {
     }
 
     public void updateMeasuredBounds(int width, int height) {
-        getBounds().setSize(Math.max(width, 0), Math.max(height, 0));
+        bounds.setSize(Math.max(width, 0), Math.max(height, 0));
     }
 
     @Override

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

@@ -44,4 +44,40 @@ class STextTest {
         SText text = SText.create(0, 0, null);
         assertEquals(SText.PLACEHOLDER_TEXT, text.getText());
     }
+
+    @Test
+    void testUpdateMeasuredBoundsActuallyUpdatesBounds() {
+        SText text = SText.create(10, 20, "Hello");
+        text.updateMeasuredBounds(200, 30);
+        Rectangle bounds = text.getBounds();
+        assertEquals(200, bounds.width, "updateMeasuredBounds must update width");
+        assertEquals(30, bounds.height, "updateMeasuredBounds must update height");
+    }
+
+    @Test
+    void testUpdateMeasuredBoundsDoesNotChangePosition() {
+        SText text = SText.create(10, 20, "Hello");
+        text.updateMeasuredBounds(200, 30);
+        Rectangle bounds = text.getBounds();
+        assertEquals(10, bounds.x, "updateMeasuredBounds must not change x");
+        assertEquals(20, bounds.y, "updateMeasuredBounds must not change y");
+    }
+
+    @Test
+    void testUpdateMeasuredBoundsNegativeClampedToZero() {
+        SText text = SText.create(0, 0, "Hello");
+        text.updateMeasuredBounds(-5, -10);
+        Rectangle bounds = text.getBounds();
+        assertEquals(0, bounds.width, "negative width must be clamped to 0");
+        assertEquals(0, bounds.height, "negative height must be clamped to 0");
+    }
+
+    @Test
+    void testUpdateMeasuredBoundsZeroIsAllowed() {
+        SText text = SText.create(0, 0, "Hello");
+        text.updateMeasuredBounds(0, 0);
+        Rectangle bounds = text.getBounds();
+        assertEquals(0, bounds.width);
+        assertEquals(0, bounds.height);
+    }
 }