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/app/(app)/feed/index.tsx

@@ -31,9 +31,9 @@ import {
 type TabKey = 'following' | 'foryou' | 'trending';
 
 const TAB_LABELS: Record<TabKey, string> = {
-  following: 'Подписки',
-  foryou:    'Для вас',
-  trending:  'В тренде',
+  following: 'Following',
+  foryou:    'For you',
+  trending:  'Trending',
 };
 
 export default function FeedScreen() {
@@ -201,15 +201,15 @@ export default function FeedScreen() {
 
   const emptyHint = useMemo(() => {
     switch (tab) {
-      case 'following': return 'Подпишитесь на кого-нибудь, чтобы увидеть их посты здесь.';
-      case 'foryou':    return 'Пока нет рекомендаций — возвращайтесь позже.';
-      case 'trending':  return 'В этой ленте пока тихо.';
+      case 'following': return 'Follow someone to see their posts here.';
+      case 'foryou':    return 'No recommendations yet — come back later.';
+      case 'trending':  return 'Nothing trending yet.';
     }
   }, [tab]);
 
   return (
     <View style={{ flex: 1, backgroundColor: '#000000', paddingTop: insets.top }}>
-      <TabHeader title="Лента" />
+      <TabHeader title="Feed" />
 
       {/* Tab strip — три таба, равномерно распределены по ширине
           (justifyContent: space-between). Каждый Pressable hug'ает
@@ -305,14 +305,14 @@ export default function FeedScreen() {
           ) : error ? (
             <EmptyState
               icon="alert-circle-outline"
-              title="Не удалось загрузить ленту"
+              title="Couldn't load feed"
               subtitle={error}
               onRetry={() => loadPosts(false)}
             />
           ) : (
             <EmptyState
               icon="newspaper-outline"
-              title="Здесь пока пусто"
+              title="Nothing to show yet"
               subtitle={emptyHint}
             />
           )
@@ -409,7 +409,7 @@ function EmptyState({
           })}
         >
           <Text style={{ color: '#ffffff', fontWeight: '700', fontSize: 13 }}>
-            Попробовать снова
+            Try again
           </Text>
         </Pressable>
       )}