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/PostCard.tsx

@@ -109,7 +109,7 @@ function PostCardInner({ post, likedByMe, onStatsChanged, onDeleted, compact }:
       // Roll back optimistic update.
       setLocalLiked(wasLiked);
       setLocalLikeCount(c => c + (wasLiked ? 1 : -1));
-      Alert.alert('Не удалось', String(e?.message ?? e));
+      Alert.alert('Failed', String(e?.message ?? e));
     } finally {
       setBusy(false);
     }
@@ -128,13 +128,13 @@ function PostCardInner({ post, likedByMe, onStatsChanged, onDeleted, compact }:
     const options: Array<{ label: string; destructive?: boolean; onPress: () => void }> = [];
     if (mine) {
       options.push({
-        label: 'Удалить пост',
+        label: 'Delete post',
         destructive: true,
         onPress: () => {
-          Alert.alert('Удалить пост?', 'Это действие нельзя отменить.', [
-            { text: 'Отмена', style: 'cancel' },
+          Alert.alert('Delete post?', 'This action cannot be undone.', [
+            { text: 'Cancel', style: 'cancel' },
             {
-              text: 'Удалить',
+              text: 'Delete',
               style: 'destructive',
               onPress: async () => {
                 try {
@@ -145,7 +145,7 @@ function PostCardInner({ post, likedByMe, onStatsChanged, onDeleted, compact }:
                   });
                   onDeleted?.(post.post_id);
                 } catch (e: any) {
-                  Alert.alert('Ошибка', String(e?.message ?? e));
+                  Alert.alert('Error', String(e?.message ?? e));
                 }
               },
             },
@@ -160,9 +160,9 @@ function PostCardInner({ post, likedByMe, onStatsChanged, onDeleted, compact }:
         style: (o.destructive ? 'destructive' : 'default') as 'default' | 'destructive',
         onPress: o.onPress,
       })),
-      { text: 'Отмена', style: 'cancel' as const },
+      { text: 'Cancel', style: 'cancel' as const },
     ];
-    Alert.alert('Действия', '', buttons);
+    Alert.alert('Actions', '', buttons);
   }, [keyFile, mine, post.post_id, onDeleted]);
 
   // Attachment preview URL — native Image can stream straight from the