Stage 7 polish: game rework + board zoom + tests (Parts D/E/F/I)

- Board: fixed-viewport transform-scale zoom (animated) with counter-scaled cqw labels, corner letters, bonus-label modes (boardlabels), contrasting grid lines
- Game: Screen shell + game tab-bar (Draw/Skip/Hint/Shuffle) via HoldConfirm popovers; MakeMove 🏁 + compact popup; rack collapses used slots; hint places tiles on board (placementFromHint) + no_hint_available toast; Scores:N replaces Hints; history slide-down (swipe/click, scroll-locked); check-word alphabet/length limit + in-memory cache + 5s throttle
- backend: no_hint_available result code split + test
- vitest: banner rotator + linkify, resultBadge, boardlabels, placementFromHint (29 tests); Playwright smoke updated; prod bundle ~74 KB gzip

ui/e2e/smoke.spec.ts

@@ -22,8 +22,9 @@ test('guest reaches a board and previews a placement', async ({ page }) => {
   await rackTile.click();
   await page.locator('[data-cell]:not(.filled)').nth(30).click();
   await expect(page.locator('[data-cell].pending')).toHaveCount(1);
-  await expect(page.locator('.preview')).toContainText(/\d/);
+  // The score preview appears where the hints count used to be.
+  await expect(page.locator('.scores')).toContainText(/\d/);
 
-  // The contextual MakeMove control appears once a tile is pending.
-  await expect(page.getByRole('button', { name: /make move/i })).toBeVisible();
+  // The contextual MakeMove control (🏁) appears once a tile is pending.
+  await expect(page.locator('.make')).toBeVisible();
 });