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/game/Rack.svelte

@@ -15,45 +15,41 @@
     selected: number | null;
     ondown: (e: PointerEvent, index: number) => void;
   } = $props();
+
+  // Used slots are hidden (the rack shifts left, freeing room on the right for the
+  // MakeMove control); the slot still exists in the model for per-tile recall.
+  const visible = $derived(slots.filter((s) => !s.used));
 </script>
 
 <div class="rack">
-  {#each slots as slot (slot.index)}
-    {#if slot.used}
-      <span class="slot empty"></span>
-    {:else}
-      <button
-        class="slot tile"
-        class:selected={selected === slot.index}
-        data-rack-index={slot.index}
-        onpointerdown={(e) => ondown(e, slot.index)}
-      >
-        <span class="letter">{slot.letter === BLANK ? '' : slot.letter}</span>
-        {#if slot.letter !== BLANK}<span class="val">{tileValue(variant, slot.letter)}</span>{/if}
-      </button>
-    {/if}
+  {#each visible as slot (slot.index)}
+    <button
+      class="tile"
+      class:selected={selected === slot.index}
+      data-rack-index={slot.index}
+      onpointerdown={(e) => ondown(e, slot.index)}
+    >
+      <span class="letter">{slot.letter === BLANK ? '' : slot.letter}</span>
+      {#if slot.letter !== BLANK}<span class="val">{tileValue(variant, slot.letter)}</span>{/if}
+    </button>
   {/each}
 </div>
 
 <style>
   .rack {
-    display: grid;
-    grid-template-columns: repeat(7, 1fr);
+    display: flex;
     gap: 5px;
-  }
-  .slot {
-    aspect-ratio: 1;
-    border-radius: 5px;
-  }
-  .empty {
-    background: var(--surface-2);
-    border: 1px dashed var(--border);
+    align-items: center;
   }
   .tile {
     position: relative;
+    flex: 0 0 auto;
+    width: min(12.5vw, 46px);
+    aspect-ratio: 1;
     background: var(--tile-bg);
     color: var(--tile-text);
     border: none;
+    border-radius: 5px;
     box-shadow: inset 0 -3px 0 var(--tile-edge);
     font-weight: 700;
     font-size: 1.4rem;
@@ -64,9 +60,14 @@
     outline: 3px solid var(--accent);
     outline-offset: -3px;
   }
+  .letter {
+    position: absolute;
+    top: 8%;
+    left: 14%;
+  }
   .val {
     position: absolute;
-    right: 3px;
+    right: 4px;
     bottom: 1px;
     font-size: 0.7rem;
     font-weight: 600;