feat(ui): merge Exchange/Pass into one action; drop dead Tournaments tab

Lobby: remove the inert 🏆 Tournaments tab (it only raised a 'coming soon' toast); the lobby is back to three tabs, matching docs/FUNCTIONAL.md.

Game: fold the separate 🥺 Skip (pass) tab into the 🔄 tab, now Exchange/Pass. Its dialog passes when no tile is selected (button 'Pass without exchanging') and exchanges when tiles are ('Exchange N'). The tab is no longer gated on an empty bag (pass must stay reachable in the endgame); inside the dialog tile selection is disabled while the bag is below a full rack (bagLen >= RACK_SIZE).

The merge is UI-only. A pass is NOT an exchange of zero tiles: the rules allow an exchange only with a full rack left in the bag and forbid a zero-tile swap, while a pass is always legal; GCG (Poslfit) writes a pass as a bare '-' and an exchange as '-TILES'. Pass and exchange stay distinct end-to-end (wire, engine, history/GCG); the dialog dispatches the existing gateway.pass / gateway.exchange. No backend/wire/history/GCG change.

Docs: docs/UI_DESIGN.md, docs/FUNCTIONAL.md (+_ru), PRERELEASE.md. Tests: ui/e2e/game.spec.ts.

ui/src/lib/i18n/en.ts

@@ -30,7 +30,6 @@ export const en = {
   'lobby.noFinished': 'No finished games yet.',
   'lobby.new': 'New',
   'lobby.stats': 'Stats',
-  'lobby.tournaments': 'Tourn.',
   'lobby.profile': 'Profile',
   'lobby.settings': 'Settings',
   'lobby.about': 'About',
@@ -38,7 +37,6 @@ export const en = {
   'lobby.theirTurn': 'Their turn',
   'lobby.hideGame': 'Remove from list',
   'lobby.vs': 'vs {opponents}',
-  'lobby.soon': 'Coming soon',
 
   'new.title': 'New game',
   'new.subtitle': 'Auto-match with another player',
@@ -63,8 +61,7 @@ export const en = {
   'game.waiting': "Waiting for {name}",
   'game.makeMove': 'Make move',
   'game.reset': 'Reset',
-  'game.draw': 'Draw',
-  'game.skip': 'Skip',
+  'game.draw': 'Exchange/Pass',
   'game.shuffle': 'Shuffle',
   'game.hint': 'Hint',
   'game.chat': 'Chat',
@@ -75,8 +72,9 @@ export const en = {
   'game.previewIllegal': 'Not a legal move',
   'game.oneWordRule': 'One word per turn',
   'game.chooseBlank': 'Choose a letter for the blank',
-  'game.exchangeTitle': 'Select tiles to exchange',
+  'game.exchangeTitle': 'Exchange or pass',
   'game.exchangeConfirm': 'Exchange {n}',
+  'game.passNoExchange': 'Pass without exchanging',
   'game.confirmResign': 'Resign this game?',
   'game.hintShown': 'Best move: {word} for {n}',
   'game.over': 'Game over',