UI: fix last-move highlight, localize move history, clamp zoom overscroll

- Highlight tracks the last move overall (not the last word): a trailing
  pass/exchange now highlights nothing, so the board no longer lights up the
  opponent's old word after our own empty move.
- Make the highlight event-driven: refreshed only on a real game event
  (open/refresh, opponent move, our own committed move) and dismissed the moment
  composing starts, so recalling a just-placed tile never re-triggers it.
- Localize non-play move-history labels via new move.* catalog keys
  (pass/exchange/resign/timeout); the label printed the raw English action.
- Clamp the zoomed board's pan at its edge (overscroll-behavior: none), removing
  the native rubber-band past the content.

Tests: lastMoveCells unit coverage (trailing pass/exchange -> empty), i18n RU
label assertions, an e2e overscroll-contract check on the zoomed viewport.

ui/e2e/zoom.spec.ts

@@ -24,3 +24,31 @@ test('zoom enlarges the board labels with the board', async ({ page }) => {
   const zoomed = await letter.evaluate((el) => parseFloat(getComputedStyle(el).fontSize));
   expect(zoomed).toBeGreaterThan(base * 1.4);
 });
+
+// Item 4 (UX): the zoomed board clamps at its edge — no native rubber-band/overscroll past
+// the content. We assert the CSS contract on the zoomed scroll container, which is
+// deterministic across engines (the bounce gesture itself is a native compositor behaviour
+// Playwright cannot reliably synthesize).
+test('zoomed board clamps overscroll at the edge', async ({ page }) => {
+  await page.goto('/');
+  await page.getByRole('button', { name: /guest/i }).click();
+  await page.getByRole('button', { name: /Ann/ }).click();
+
+  // Double-tap an empty cell to zoom in.
+  await page
+    .locator('[data-cell]:not(.filled)')
+    .nth(20)
+    .evaluate((el: HTMLElement) => {
+      el.click();
+      el.click();
+    });
+
+  const viewport = page.locator('.viewport.zoomed');
+  await expect(viewport).toBeVisible();
+  const ob = await viewport.evaluate((el) => {
+    const s = getComputedStyle(el);
+    return { x: s.overscrollBehaviorX, y: s.overscrollBehaviorY };
+  });
+  expect(ob.x).toBe('none');
+  expect(ob.y).toBe('none');
+});