Stage 7 polish (round 3): zoom magnifies labels, popover edge-anchor, flash x2

- item 5: move container-type to the zoom-scaled .scaler so cqw labels grow WITH the board (magnifying-glass zoom); new e2e measures the font grows ~1.85x
- item 8: confirm popovers anchor to the trigger's right edge (no longer run off-screen)
- item 9: last-word flash runs 2 cycles then settles to normal (was infinite)

ui/e2e/zoom.spec.ts

@@ -0,0 +1,26 @@
+import { expect, test } from '@playwright/test';
+
+// Item 5: zooming the board must enlarge the labels too (a magnifying-glass zoom).
+// cqw is sized against the zoom-scaled board, so the font grows with the cells.
+test('zoom enlarges the board labels with the board', async ({ page }) => {
+  await page.goto('/');
+  await page.getByRole('button', { name: /guest/i }).click();
+  await page.getByRole('button', { name: /Ann/ }).click();
+
+  const letter = page.locator('[data-cell] .letter').first();
+  await expect(letter).toBeVisible();
+  const base = await letter.evaluate((el) => parseFloat(getComputedStyle(el).fontSize));
+
+  // Double-tap an empty cell to zoom in (two synchronous clicks = a double-tap).
+  await page
+    .locator('[data-cell]:not(.filled)')
+    .nth(20)
+    .evaluate((el: HTMLElement) => {
+      el.click();
+      el.click();
+    });
+  await page.waitForTimeout(400); // let the width transition settle
+
+  const zoomed = await letter.evaluate((el) => parseFloat(getComputedStyle(el).fontSize));
+  expect(zoomed).toBeGreaterThan(base * 1.4);
+});