chore(client): translate all user-visible strings to English

Mixed-language UI was confusing — onboarding said "Why DChain / How it
works / Your keys" in English headings but feature descriptions and
CTAs were in Russian; compose's confirm dialog was Russian; feed tabs
were Russian; error messages in humanizeTxError were Russian.
Everything user-facing is now English.

Files touched (only string literals, not comments):
  app/index.tsx              onboarding slides + CTA buttons
  app/(app)/compose.tsx      composer alerts, header button, placeholder,
                             attachment-size hint
  app/(app)/feed/index.tsx   tab labels (Following/For you/Trending),
                             empty-state hints, retry button
  app/(app)/feed/[id].tsx    post detail header + stats rows (Views,
                             Likes, Size, Paid to publish, Hosted on,
                             Hashtags)
  app/(app)/feed/tag/[tag].tsx  empty-state copy
  app/(app)/profile/[address].tsx  Profile header, Follow/Following,
                             Edit, Open chat, Address, Copied, Encryption,
                             Added, Members, unknown-contact hint
  app/(app)/new-contact.tsx  Search title, placeholder, Search button,
                             empty-state hint, E2E-ready indicator,
                             Intro label + placeholder, fee-tier labels
                             (Min / Standard / Priority), Send request,
                             Insufficient-balance alert, Request-sent
                             alert
  app/(app)/requests.tsx     Notifications title, empty-state, Accept /
                             Decline buttons, decline-confirm alert,
                             "wants to add you" line
  components/SearchBar.tsx   default placeholder
  components/feed/PostCard.tsx  long-press menu (Delete post, confirm,
                             Actions / Cancel)
  components/feed/ShareSheet.tsx  sheet title, contact-search placeholder,
                             empty state, Select contacts / Send button,
                             plural helper rewritten for English
  components/chat/PostRefCard.tsx  "POST" ribbon, "photo" indicator
  lib/api.ts                 humanizeTxError (rate-limit, clock skew,
                             bad signature, 400/5xx/network-error
                             messages)
  lib/dates.ts               dateBucket now returns Today/Yesterday/
                             "Jun 17, 2025"; month array switched to
                             English short forms

Code comments left in Russian intentionally — they're developer
context, not user-facing. This commit is purely display-string.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

client-app/lib/dates.ts

@@ -5,10 +5,10 @@
  * который тоже в секундах). Для ms-таймштампов делаем нормализацию внутри.
  */
 
-// ─── Русские месяцы (genitive для "17 июня 2025") ────────────────────────────
-const RU_MONTHS_GEN = [
-  'января', 'февраля', 'марта',  'апреля', 'мая',     'июня',
-  'июля',   'августа', 'сентября', 'октября', 'ноября', 'декабря',
+// English short month names ("Jun 17, 2025").
+const MONTHS_SHORT = [
+  'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
+  'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec',
 ];
 
 function sameDay(a: Date, b: Date): boolean {
@@ -20,8 +20,8 @@ function sameDay(a: Date, b: Date): boolean {
 }
 
 /**
- * Day-bucket label для сепараторов внутри чата.
- *   "Сегодня" / "Вчера" / "17 июня 2025"
+ * Day-bucket label for chat separators.
+ *   "Today" / "Yesterday" / "Jun 17, 2025"
  *
  * @param ts unix-seconds
  */
@@ -29,9 +29,9 @@ export function dateBucket(ts: number): string {
   const d = new Date(ts * 1000);
   const now = new Date();
   const yday = new Date(); yday.setDate(now.getDate() - 1);
-  if (sameDay(d, now))  return 'Сегодня';
-  if (sameDay(d, yday)) return 'Вчера';
-  return `${d.getDate()} ${RU_MONTHS_GEN[d.getMonth()]} ${d.getFullYear()}`;
+  if (sameDay(d, now))  return 'Today';
+  if (sameDay(d, yday)) return 'Yesterday';
+  return `${MONTHS_SHORT[d.getMonth()]} ${d.getDate()}, ${d.getFullYear()}`;
 }
 
 /**