Stage 17 #2: extend the offline soft-disable to all server-action buttons

Following the in-game bar, the Connecting indicator now also visually disables the
other proactive (server-sending) controls while offline: chat send + nudge, profile
save / link email|telegram / merge-confirm, friends (redeem, get-code, accept/decline,
unfriend, block, unblock), New Game (auto-match variant + send-invitation) and the
lobby hide ❌. Purely local controls (board/rack/reset, menus, navigation, settings,
copy-code) stay live. Each reads the global connection.online signal; full e2e + check
green.

ui/src/game/Game.svelte

@@ -794,7 +794,7 @@
   <Modal title={t('game.confirmResign')} onclose={() => (resignOpen = false)}>
     <div class="confirm-row">
       <button class="cancel" onclick={() => (resignOpen = false)}>{t('common.cancel')}</button>
-      <button class="danger" onclick={doResign}>{t('game.dropGame')}</button>
+      <button class="danger" onclick={doResign} disabled={!connection.online}>{t('game.dropGame')}</button>
     </div>
   </Modal>
 {/if}