fix: make dashboard widgets closable (#14)

Every GridStackItem now renders a close button next to its drag grip,
mirroring the grip's hover affordance. Closing detaches the item
server-side; grid-stack.ts already unregisters widgets via its
MutationObserver, so the layout is persisted without an extra protocol.

Closable is on by default and can be turned off per item with
setClosable(false); GridStackItem.CloseEvent lets views react.

The GridStackView "remove last" toolbar button is dropped — per-widget
close replaces it, so the view no longer tracks a widget stack. Its
counter now only grows, keeping a closed widget's id from being handed
to a new widget (which would inherit the saved position).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ue9ZtWUBQF4SuSHpzZ3zwq

src/test/java/com/example/views/GridStackViewTest.java

@@ -5,13 +5,18 @@ import com.example.components.GridStackItem;
 import com.example.components.GridStackLayout;
 import com.vaadin.browserless.SpringBrowserlessTest;
 import com.vaadin.browserless.ViewPackages;
+import com.vaadin.browserless.internal.ElementUtilsKt;
 import com.vaadin.flow.component.button.Button;
+import com.vaadin.flow.component.html.Div;
+import com.vaadin.flow.dom.DomEvent;
+import com.vaadin.flow.internal.JacksonUtils;
 import org.junit.jupiter.api.Test;
 import org.springframework.boot.test.context.SpringBootTest;
 
 import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -32,7 +37,7 @@ class GridStackViewTest extends SpringBrowserlessTest {
     }
 
     @Test
-    void addAndRemoveWidget_changesItemCount() {
+    void addAndCloseWidget_changesItemCount() {
         navigate(GridStackView.class);
 
         GridStackLayout grid = $view(GridStackLayout.class).first();
@@ -41,18 +46,59 @@ class GridStackViewTest extends SpringBrowserlessTest {
         button("gridstack.addWidget").click();
         assertEquals(initial + 1, grid.getLayout().size());
 
-        button("gridstack.removeWidget").click();
+        clickCloseButton($view(GridStackItem.class).last());
         assertEquals(initial, grid.getLayout().size());
     }
 
     @Test
-    void removeWidget_onDefaultLayout_keepsStaticWidgets() {
+    void closeButton_removesTheClickedWidgetOnly() {
         navigate(GridStackView.class);
 
         GridStackLayout grid = $view(GridStackLayout.class).first();
-        button("gridstack.removeWidget").click();
+        GridStackItem first = $view(GridStackItem.class).first();
+        String closedId = first.getItemId();
 
-        assertEquals(4, grid.getLayout().size(), "static widgets must not be removable");
+        clickCloseButton(first);
+
+        List<GridStackItem.Position> layout = grid.getLayout();
+        assertEquals(3, layout.size());
+        assertFalse(layout.stream().anyMatch(p -> closedId.equals(p.id())),
+                "the closed widget must be gone from the layout");
+    }
+
+    @Test
+    void closeListener_firesOnceItemIsDetached() {
+        navigate(GridStackView.class);
+
+        GridStackLayout grid = $view(GridStackLayout.class).first();
+        GridStackItem item = $view(GridStackItem.class).first();
+        int[] fired = {0};
+        item.addCloseListener(e -> fired[0]++);
+
+        item.close();
+
+        assertEquals(1, fired[0]);
+        assertEquals(3, grid.getLayout().size());
+    }
+
+    @Test
+    void nonClosableItem_hasNoCloseButton() {
+        navigate(GridStackView.class);
+
+        GridStackItem item = $view(GridStackItem.class).first();
+        assertTrue(item.isClosable(), "items are closable by default");
+
+        item.setClosable(false);
+        assertFalse(item.isClosable());
+        assertFalse(item.getChildren().anyMatch(child -> child == item.getCloseButton()));
+    }
+
+    /** Fires the DOM click the close button listens for, rather than calling
+     *  {@code close()} directly, so the button's own wiring is covered too. */
+    private void clickCloseButton(GridStackItem item) {
+        Div closeButton = item.getCloseButton();
+        ElementUtilsKt._fireDomEvent(closeButton.getElement(),
+                new DomEvent(closeButton.getElement(), "click", JacksonUtils.createObjectNode()));
     }
 
     private Button button(String translationKey) {