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/src/lib/banner.test.ts

@@ -0,0 +1,46 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { createBannerRotator, defaultBannerConfig, linkify } from './banner';
+
+describe('linkify', () => {
+  it('escapes html and renders markdown links', () => {
+    expect(linkify('a < b & c')).toBe('a &lt; b &amp; c');
+    expect(linkify('see [docs](https://x.com) now')).toBe(
+      'see <a href="https://x.com" target="_blank" rel="noopener noreferrer">docs</a> now',
+    );
+  });
+  it('drops a non-http(s) link target (keeps the label)', () => {
+    expect(linkify('[x](ftp://evil)')).toBe('x');
+    expect(linkify('[y](javascript:boom)')).toBe('y');
+  });
+});
+
+describe('banner rotator', () => {
+  afterEach(() => vi.useRealTimers());
+
+  it('holds a fitting message then advances, and scrolls an overflowing one', () => {
+    vi.useFakeTimers();
+    const cfg = { ...defaultBannerConfig, holdMs: 1000, edgePauseMs: 100, fadeMs: 10, scrollPxPerSec: 50 };
+    const shown: number[] = [];
+    let scrolled = 0;
+    const overflow = [0, 200]; // item 0 fits, item 1 overflows
+    const r = createBannerRotator(
+      [{ md: 'a' }, { md: 'b' }],
+      {
+        overflowPx: (i) => overflow[i],
+        show: (i) => shown.push(i),
+        scrollTo: () => scrolled++,
+      },
+      cfg,
+    );
+
+    r.start();
+    expect(shown).toEqual([0]);
+    vi.advanceTimersByTime(cfg.fadeMs); // settle + measure item 0
+    vi.advanceTimersByTime(cfg.holdMs); // advance to item 1
+    expect(shown).toEqual([0, 1]);
+    vi.advanceTimersByTime(cfg.fadeMs); // settle + measure item 1 (overflows)
+    vi.advanceTimersByTime(cfg.edgePauseMs); // edge pause -> scrollTo
+    expect(scrolled).toBe(1);
+    r.stop();
+  });
+});