fix(game): own export chooser modal; PNG option outside in-app webviews only

Telegram's native showPopup delivers its callback with no user
activation, so navigator.share (TG iOS) and clipboard writes (TG
Android GCG copy) silently fail from it — the chooser is now always the
app's own modal, keeping the button click's gesture alive for the
delivery APIs.

The data:URL preview modal is dropped: the Android TG/VK long-press
menu mangles data: URLs (dead download, black-screen open, base64
clipboard garbage), so a binary PNG has no working client-side route in
those webviews at all. The image option is withheld there until the
server-rendered signed-URL delivery (Telegram downloadFile /
VKWebAppDownloadFile) lands; the plain web and mobile browsers keep it.

On-device findings by the owner on the test contour (TG iOS, TG
Android, VK Android).

ui/src/lib/i18n/en.ts

@@ -311,12 +311,8 @@ export const en = {
   'stats.guestHint': 'Sign in to track your statistics.',
 
   'game.exportGcg': 'Export game',
-  'game.exportChoice': 'Export the finished game as:',
   'game.exportImageOpt': 'Image (PNG)',
   'game.exportGcgOpt': 'GCG file',
-  'game.imageSaveHint': 'Long-press (or right-click) the image to save it.',
-  'game.imageCopy': 'Copy image',
-  'game.imageCopied': 'Image copied to the clipboard.',
   'game.gcgActiveOnly': 'Available once the game is finished.',
   'game.gcgCopied': 'GCG copied to the clipboard.',
   'game.addFriendShort': 'Add friend?',

ui/src/lib/i18n/ru.ts

@@ -311,12 +311,8 @@ export const ru: Record<MessageKey, string> = {
   'stats.guestHint': 'Войдите, чтобы вести статистику.',
 
   'game.exportGcg': 'Экспорт партии',
-  'game.exportChoice': 'Экспортировать завершённую партию как:',
   'game.exportImageOpt': 'Картинка (PNG)',
   'game.exportGcgOpt': 'Файл GCG',
-  'game.imageSaveHint': 'Чтобы сохранить картинку — долгое нажатие (или правый клик).',
-  'game.imageCopy': 'Скопировать картинку',
-  'game.imageCopied': 'Картинка скопирована в буфер обмена.',
   'game.gcgActiveOnly': 'Доступно после завершения игры.',
   'game.gcgCopied': 'GCG скопирован в буфер обмена.',
   'game.addFriendShort': 'В друзья?',