fix(ui): per-bot invite caption + friendly self-redeem note

- The share caption is now in the bot's language: 'Давай играть в Эрудит!' (ru bot),
  "Let's play Scrabble!" (en bot) — picked by the session service language, not the
  interface language.
- Redeeming your own invite (deep link or manual) no longer shows the scary
  'can't do that to yourself' error; it shows a friendly neutral note instead.

ui/src/screens/Friends.svelte

@@ -3,7 +3,9 @@
   import { app, handleError, refreshNotifications, showToast } from '../lib/app.svelte';
   import { connection } from '../lib/connection.svelte';
   import { gateway } from '../lib/gateway';
-  import { t } from '../lib/i18n/index.svelte';
+  import { GatewayError } from '../lib/client';
+  import { localeFrom, t } from '../lib/i18n/index.svelte';
+  import { translate } from '../lib/i18n/catalog';
   import { friendCodeParam, shareLink } from '../lib/deeplink';
   import { shareTelegramLink } from '../lib/telegram';
   import type { AccountRef, FriendCode } from '../lib/model';
@@ -62,7 +64,11 @@
       showToast(t('friends.added', { name: friend.displayName }));
       await load();
     } catch (e) {
-      handleError(e);
+      if (e instanceof GatewayError && e.code === 'self_relation') {
+        showToast(t('friends.selfInvite')); // redeeming your own code: a friendly, non-error note
+      } else {
+        handleError(e);
+      }
     }
   }
 
@@ -83,8 +89,10 @@
   // shareInvite shares the friend-code deep link: inside Telegram via the native
   // "share to chat" picker; on the web via the system share sheet; failing both, it
   // copies the link to the clipboard.
-  async function shareInvite(url: string) {
-    const text = t('friends.inviteText');
+  async function shareInvite(url: string, lang: string) {
+    // The caption is in the bot's language (Эрудит for ru, Scrabble for en), not the
+    // interface language — the recipient lands in that bot.
+    const text = translate(localeFrom(lang), 'friends.inviteText');
     if (shareTelegramLink(url, text)) return;
     if (typeof navigator !== 'undefined' && navigator.share) {
       try {
@@ -120,7 +128,8 @@
         <button class="btn" onclick={redeem} disabled={!connection.online}>{t('friends.redeem')}</button>
       </div>
       {#if code}
-        {@const tg = shareLink(friendCodeParam(code.code), app.session?.serviceLanguage || app.locale)}
+        {@const lang = app.session?.serviceLanguage || app.locale}
+        {@const tg = shareLink(friendCodeParam(code.code), lang)}
         <div class="code" data-testid="friend-code">
           <div class="coderow">
             <button class="codeval" onclick={copyCode}>{code.code}</button>
@@ -130,7 +139,7 @@
             {t('friends.codeHint')} · {t('friends.codeExpires', { time: codeTime(code.expiresAtUnix) })}
           </span>
           {#if tg}
-            <button type="button" class="link tgshare" onclick={() => shareInvite(tg)}>{t('friends.shareTelegram')}</button>
+            <button type="button" class="link tgshare" onclick={() => shareInvite(tg, lang)}>{t('friends.shareTelegram')}</button>
           {/if}
         </div>
       {:else}