fix: update ApexCharts data in place instead of re-rendering (#23)

Every data change went through renderChart, which rebuilt the chart from a
full option set: animations restarted and zoom/selection state was lost.

Add an updateData path that patches the live chart via ApexCharts'
updateSeries (and updateOptions only when categories/labels actually
change), exposed as AxisChart.updateData / PieChart.updateData. Before the
first render there is nothing to patch, so those fall back to setData.
The theme overlay is re-applied to the merged options, so a rebuild after
a detach starts from the patched data.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0124BiJikbhbiEsNfJxdWM69

src/test/java/com/example/e2e/DashboardChartPlaywrightTest.java

@@ -0,0 +1,58 @@
+package com.example.e2e;
+
+import com.microsoft.playwright.Locator;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static com.microsoft.playwright.assertions.PlaywrightAssertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * End-to-end coverage for the incremental update path of {@code apex-chart.ts}:
+ * a data update must patch the running ApexCharts instance instead of tearing
+ * the chart down and building it again.
+ */
+class DashboardChartPlaywrightTest extends PlaywrightTestBase {
+
+    private static final String PATCH = """
+            {"series":[{"name":"Revenue","data":[1,2,3,4,5,6]}],
+             "categories":["Jan","Feb","Mar","Apr","May","Jun"]}""";
+
+    @BeforeEach
+    void openDashboard() {
+        navigate("");
+    }
+
+    @Test
+    void dataUpdate_keepsTheRenderedSvgInPlace() {
+        Locator chart = page.locator("apex-chart").first();
+        assertThat(chart.locator("svg").first()).isVisible();
+
+        // Tag the live SVG node: a full rebuild would replace it and drop the tag.
+        chart.evaluate("el => el.querySelector('svg').dataset.marker = 'first-render'");
+
+        chart.evaluate("(el, patch) => el.updateData(patch)", PATCH);
+
+        assertEquals(1, chart.locator("svg[data-marker='first-render']").count(),
+                "the chart must be patched in place, not recreated");
+        assertEquals("1,2,3,4,5,6",
+                chart.evaluate("el => JSON.parse(el.lastOptionsJson).series[0].data.join(',')"),
+                "the patched data must have reached the chart");
+    }
+
+    @Test
+    void dataUpdate_keepsTheThemeOverlay() {
+        Locator chart = page.locator("apex-chart").first();
+        assertThat(chart.locator("svg").first()).isVisible();
+
+        chart.evaluate("(el, patch) => el.updateData(patch)", PATCH);
+
+        // grid.borderColor is only ever set by applyThemeOverlay(), from the
+        // resolved --dialect-border token — so a resolved rgb() value here means
+        // the overlay survived the incremental update.
+        Object borderColor = chart.evaluate("el => JSON.parse(el.lastOptionsJson).grid.borderColor");
+        assertTrue(String.valueOf(borderColor).startsWith("rgb"),
+                "expected a resolved theme color, got: " + borderColor);
+    }
+}