feat(ui): Erudit blank tiles carry the star (✻) mark

The Erudit variant's blank is the "звёздочка", so render it with a star.
An empty rack blank (and its drag ghost) shows ✻ centred; a placed blank
keeps its designated letter and carries ✻ where the (absent) point value
sits — on the board and in the Stats best-move tiles. The Scrabble variants
are unchanged. Gated by usesStarBlank() in lib/variants.ts.

ui/src/screens/Stats.svelte

@@ -73,7 +73,7 @@
             {#each bestMoves as bm (bm.variant)}
               <span class="variant">{t(variantNameKey(bm.variant))}</span>
               <span class="score">{bm.score}</span>
-              <span class="wordcell"><WordTiles word={bm.word} /></span>
+              <span class="wordcell"><WordTiles word={bm.word} variant={bm.variant} /></span>
             {/each}
           </div>
         </div>