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/i18n/en.ts

@@ -88,6 +88,11 @@ export const en = {
   'game.noHintOptions': 'No options with your letters.',
   'game.scores': 'Scores: {n}',
 
+  'move.pass': 'Pass',
+  'move.exchange': 'Exchange',
+  'move.resign': 'Resigned',
+  'move.timeout': 'Timed out',
+
   'result.victory': 'Victory',
   'result.defeat': 'Defeat',
   'result.draw': 'Draw',