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/components/feed/ShareSheet.tsx

@@ -74,14 +74,14 @@ export function ShareSheet({ visible, post, onClose }: ShareSheetProps) {
         post, contacts: targets, keyFile,
       });
       if (failed > 0) {
-        Alert.alert('Готово', `Отправлено в ${ok} из ${ok + failed} чат${plural(ok + failed)}.`);
+        Alert.alert('Done', `Sent to ${ok} of ${ok + failed} ${plural(ok + failed)}.`);
       }
       // Close + reset regardless — done is done.
       setPicked(new Set());
       setQuery('');
       onClose();
     } catch (e: any) {
-      Alert.alert('Не удалось', String(e?.message ?? e));
+      Alert.alert('Failed', String(e?.message ?? e));
     } finally {
       setSending(false);
     }
@@ -136,7 +136,7 @@ export function ShareSheet({ visible, post, onClose }: ShareSheetProps) {
             paddingHorizontal: 16, marginBottom: 10,
           }}>
             <Text style={{ color: '#ffffff', fontSize: 17, fontWeight: '700' }}>
-              Поделиться постом
+              Share post
             </Text>
             <View style={{ flex: 1 }} />
             <Pressable onPress={closeAndReset} hitSlop={8}>
@@ -158,7 +158,7 @@ export function ShareSheet({ visible, post, onClose }: ShareSheetProps) {
               <TextInput
                 value={query}
                 onChangeText={setQuery}
-                placeholder="Поиск по контактам"
+                placeholder="Search contacts"
                 placeholderTextColor="#5a5a5a"
                 style={{
                   flex: 1,
@@ -196,8 +196,8 @@ export function ShareSheet({ visible, post, onClose }: ShareSheetProps) {
                 <Ionicons name="people-outline" size={28} color="#5a5a5a" />
                 <Text style={{ color: '#8b8b8b', fontSize: 13, marginTop: 10 }}>
                   {query.length > 0
-                    ? 'Нет контактов по такому запросу'
-                    : 'Контакты с ключами шифрования отсутствуют'}
+                    ? 'No contacts match this search'
+                    : 'No contacts with encryption keys yet'}
                 </Text>
               </View>
             }
@@ -227,8 +227,8 @@ export function ShareSheet({ visible, post, onClose }: ShareSheetProps) {
                   fontSize: 14,
                 }}>
                   {picked.size === 0
-                    ? 'Выберите контакты'
-                    : `Отправить (${picked.size})`}
+                    ? 'Select contacts'
+                    : `Send (${picked.size})`}
                 </Text>
               )}
             </Pressable>
@@ -298,10 +298,5 @@ function shortAddr(a: string, n = 6): string {
 }
 
 function plural(n: number): string {
-  const mod100 = n % 100;
-  const mod10  = n % 10;
-  if (mod100 >= 11 && mod100 <= 19) return 'ов';
-  if (mod10 === 1) return '';
-  if (mod10 >= 2 && mod10 <= 4) return 'а';
-  return 'ов';
+  return n === 1 ? 'chat' : 'chats';
 }