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/placement.ts

@@ -4,7 +4,7 @@
 // payload. It is board-agnostic (the gateway/engine does full legality validation at
 // submit), which keeps it trivially unit-testable.
 
-import type { Direction } from './model';
+import type { Direction, Tile } from './model';
 import type { PlacedTile } from './client';
 
 export interface PendingTile {
@@ -36,6 +36,25 @@ export function newPlacement(rack: string[]): Placement {
   return { rack: [...rack], pending: [] };
 }
 
+/**
+ * placementFromHint turns a hint move's tiles into a pending placement by matching each
+ * tile to a rack slot (a blank "?" for blank tiles, else the matching letter), so the
+ * player sees the suggested move laid out and decides whether to commit it.
+ */
+export function placementFromHint(tiles: Tile[], rack: string[]): Placement {
+  const used = new Set<number>();
+  const pending: PendingTile[] = [];
+  const take = (pred: (letter: string, i: number) => boolean) => rack.findIndex((l, i) => !used.has(i) && pred(l, i));
+  for (const t of tiles) {
+    let idx = t.blank ? take((l) => l === BLANK) : take((l) => l === t.letter.toUpperCase());
+    if (idx < 0) idx = take((l) => l === BLANK); // fall back to a blank
+    if (idx < 0) continue;
+    used.add(idx);
+    pending.push({ rackIndex: idx, row: t.row, col: t.col, letter: t.letter.toUpperCase(), blank: rack[idx] === BLANK });
+  }
+  return { rack: [...rack], pending };
+}
+
 function usedIndexes(p: Placement): Set<number> {
   return new Set(p.pending.map((t) => t.rackIndex));
 }