test: add bbox selection overlay mode e2e test (#933)

## Summary

Adds e2e test coverage for bbox selection in overlay render mode,
validating the functionality introduced in #921.

## Changes

- Add `bbox-select-overlay.spec.ts`: test suite for overlay mode bbox
selection
- Add `maplibre.ts` helper for MapLibre-specific bbox drawing  
- Adjust timing: increase overlay init wait (2s → 5s)

## How to verify

```bash
npm run test:e2e
```

Ready for review.

Author: vgeorge

tests/e2e/bbox-select-overlay.spec.ts

@@ -0,0 +1,47 @@
+import { test, expect } from "@playwright/test";
+import {
+  openNotebookFresh,
+  runFirstNCells,
+  executeCellAndWaitForOutput,
+} from "./helpers/notebook";
+import { validateBounds } from "./helpers/assertions";
+import { drawBboxOnMapLibre } from "./helpers/maplibre";
+
+test.describe("BBox selection - Overlay render mode", () => {
+  test("draws bbox and syncs selected_bounds to Python with overlay render_mode", async ({
+    page,
+  }) => {
+    const { notebookRoot } = await openNotebookFresh(
+      page,
+      "simple-map-overlay.ipynb",
+      {
+        workspaceId: `bbox-overlay-${Date.now()}`,
+      },
+    );
+    await runFirstNCells(page, notebookRoot, 2);
+    await page.waitForTimeout(5000);
+
+    // Start bbox selection mode
+    const bboxButton = page.getByRole("button", { name: "Select BBox" });
+    await expect(bboxButton).toBeVisible({ timeout: 10000 });
+    await bboxButton.click();
+
+    // Verify drawing mode is active
+    const cancelButton = page.getByRole("button", { name: "Cancel drawing" });
+    await expect(cancelButton).toBeVisible({ timeout: 5000 });
+
+    // Draw bbox using simple mouse events
+    await drawBboxOnMapLibre(page, { x: 200, y: 200 }, { x: 400, y: 400 });
+
+    // Verify bbox was drawn successfully
+    const finalClearButton = page.getByRole("button", {
+      name: "Clear bounding box",
+    });
+    await expect(finalClearButton).toBeVisible({ timeout: 5000 });
+
+    // Execute cell to check selected bounds
+    const output = await executeCellAndWaitForOutput(notebookRoot, 2);
+    const outputText = await output.textContent();
+    validateBounds(outputText);
+  });
+});

tests/e2e/helpers/maplibre.ts

@@ -0,0 +1,28 @@
+import type { Page } from "@playwright/test";
+
+/**
+ * Draws a bounding box on the MapLibre map using click-click pattern.
+ * In overlay mode, MapLibre handles events and forwards them to deck.gl via MapboxOverlay.
+ *
+ * The bbox selection pattern matches deck-first mode: click at start, hover at end, click at end.
+ */
+export async function drawBboxOnMapLibre(
+  page: Page,
+  start: { x: number; y: number },
+  end: { x: number; y: number },
+): Promise<void> {
+  // Find the map canvas (MapLibre renders the map canvas directly)
+  const canvas = page.locator("canvas").first();
+  await canvas.waitFor({ state: "visible", timeout: 10000 });
+
+  // Bbox selection pattern: click at start, hover at end, click at end
+  // Use locator-based actions which are more robust than page.mouse
+  await canvas.click({ position: { x: start.x, y: start.y } });
+  await page.waitForTimeout(500);
+
+  await canvas.hover({ position: { x: end.x, y: end.y } });
+  await page.waitForTimeout(500);
+
+  await canvas.click({ position: { x: end.x, y: end.y } });
+  await page.waitForTimeout(1000);
+}