UI: fix last-move highlight, localize move history, clamp zoom overscroll

- Highlight tracks the last move overall (not the last word): a trailing
  pass/exchange now highlights nothing, so the board no longer lights up the
  opponent's old word after our own empty move.
- Make the highlight event-driven: refreshed only on a real game event
  (open/refresh, opponent move, our own committed move) and dismissed the moment
  composing starts, so recalling a just-placed tile never re-triggers it.
- Localize non-play move-history labels via new move.* catalog keys
  (pass/exchange/resign/timeout); the label printed the raw English action.
- Clamp the zoomed board's pan at its edge (overscroll-behavior: none), removing
  the native rubber-band past the content.

Tests: lastMoveCells unit coverage (trailing pass/exchange -> empty), i18n RU
label assertions, an e2e overscroll-contract check on the zoomed viewport.

ui/src/lib/board.ts

@@ -3,7 +3,7 @@
 // the dictionary-independent history invariant (ARCHITECTURE §9.1): apply each play's
 // placed tiles onto an empty grid.
 
-import type { MoveRecord, Tile } from './model';
+import type { MoveRecord } from './model';
 import { BOARD_SIZE } from './premiums';
 
 export interface BoardCell {
@@ -36,10 +36,11 @@ export function replay(moves: MoveRecord[]): Board {
   return b;
 }
 
-/** lastPlayTiles returns the tiles of the most recent play (for highlighting). */
-export function lastPlayTiles(moves: MoveRecord[]): Tile[] {
-  for (let i = moves.length - 1; i >= 0; i--) {
-    if (moves[i].action === 'play') return moves[i].tiles;
-  }
-  return [];
+/** lastMoveCells returns the cells of the last move's tiles (as "row,col" keys), but only
+ * when that move placed tiles (a play). A trailing pass/exchange/resign/timeout highlights
+ * nothing — the recent-move highlight tracks the last move overall, not the last word. */
+export function lastMoveCells(moves: MoveRecord[]): Set<string> {
+  const last = moves.length ? moves[moves.length - 1] : null;
+  if (!last || last.action !== 'play') return new Set();
+  return new Set(last.tiles.map((t) => `${t.row},${t.col}`));
 }