feat(client): Twitter-style social feed UI (Phase C of v2.0.0)

Ships the client side of the v2.0.0 feed feature. Folds client-app/
into the monorepo (was previously .gitignored as "tracked separately"
but no separate repo ever existed — for v2.0.0 the client is
first-class).

Feed screens

  app/(app)/feed.tsx — Feed tab
    - Three-way tab strip: Подписки / Для вас / В тренде backed by
      /feed/timeline, /feed/foryou, /feed/trending respectively
    - Default landing tab is "Для вас" — surfaces discovery without
      requiring the user to follow anyone first
    - FlatList with pull-to-refresh + viewability-driven view counter
      bump (posts visible ≥ 60% for ≥ 1s trigger POST /feed/post/…/view)
    - Floating blue compose button → /compose
    - Per-post liked_by_me fetched in batches of 6 after list load

  app/(app)/compose.tsx — post composer modal
    - Fullscreen, Twitter-like header (✕ left, Опубликовать right)
    - Auto-focused multiline TextInput, 4000 char cap
    - Hashtag preview chips that auto-update as you type
    - expo-image-picker + expo-image-manipulator pipeline: resize to
      1080px max-dim, JPEG Q=50 (client-side first-pass compression
      before the mandatory server-side scrub)
    - Live fee estimate + balance guard with a confirmation modal
      ("Опубликовать пост? Цена: 0.00X T · Размер: N KB")
    - Exif: false passed to ImagePicker as an extra privacy layer

  app/(app)/feed/[id].tsx — post detail
    - Full PostCard rendering + detailed info panel (views, likes,
      size, fee, hosting relay, hashtags as tappable chips)
    - Triggers bumpView on mount
    - 410 (on-chain soft-delete) routes back to the feed

  app/(app)/feed/tag/[tag].tsx — hashtag feed

  app/(app)/profile/[address].tsx — rebuilt
    - Twitter-ish profile: avatar, name, address short-form, post count
    - Posts | Инфо tab strip
    - Follow / Unfollow button for non-self profiles (optimistic UI)
    - Edit button on self profile → settings
    - Secondary actions (chat, copy address) when viewing a known contact

Supporting library

  lib/feed.ts — HTTP wrappers + tx builders for every /feed/* endpoint:
    - publishPost (POST /feed/publish, signed)
    - publishAndCommit (publish → on-chain CREATE_POST)
    - fetchPost / fetchStats / bumpView
    - fetchAuthorPosts / fetchTimeline / fetchForYou / fetchTrending /
      fetchHashtag
    - buildCreatePostTx / buildDeletePostTx
    - buildFollowTx / buildUnfollowTx
    - buildLikePostTx / buildUnlikePostTx
    - likePost / unlikePost / followUser / unfollowUser / deletePost
      (high-level helpers that bundle build + submitTx)
    - formatFee, formatRelativeTime, formatCount — Twitter-like display
      helpers

  components/feed/PostCard.tsx — core card component
    - Memoised for performance (N-row re-render on every like elsewhere
      would cost a lot otherwise)
    - Optimistic like toggle with heart-bounce spring animation
    - Hashtag highlighting in body text (tappable → hashtag feed)
    - Long-press context menu (Delete, owner-only)
    - Views / likes / share-link / reply icons in footer row

Navigation cleanup

  - NavBar: removed the SOON pill on the Feed tab (it's shipped now)
  - (app)/_layout: hide NavBar on /compose and /feed/* sub-routes
  - AnimatedSlot: treat /feed/<id>, /feed/tag/<t>, /compose as
    sub-routes so back-swipe-right closes them

Channel removal (client side)

  - lib/types.ts: ContactKind stripped to 'direct' | 'group'; legacy
    'channel' flag removed. `kind` field kept for backward compat with
    existing AsyncStorage records.
  - lib/devSeed.ts: dropped the 5 channel seed contacts.
  - components/ChatTile.tsx: removed channel kindIcon branch.

Dependencies

  - expo-image-manipulator added for client-side image compression.
  - expo-file-system/legacy used for readAsStringAsync (SDK 54 moved
    that API to the legacy sub-path; the new streaming API isn't yet
    stable).

Type check

  - npx tsc --noEmit — clean, 0 errors.

Next (not in this commit)

  - Direct attachment-bytes endpoint on the server so post-detail can
    actually render the image (currently shows placeholder with URL)
  - Cross-relay body fetch via /api/relays + hosting_relay pubkey
  - Mentions (@username) with notifications
  - Full-text search

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

client-app/lib/storage.ts

@@ -0,0 +1,101 @@
+/**
+ * Persistent storage for keys and app settings.
+ * On mobile: expo-secure-store for key material, AsyncStorage for settings.
+ * On web: falls back to localStorage (dev only).
+ */
+
+import * as SecureStore from 'expo-secure-store';
+import AsyncStorage from '@react-native-async-storage/async-storage';
+import type { KeyFile, Contact, NodeSettings } from './types';
+
+// ─── Keys ─────────────────────────────────────────────────────────────────────
+
+const KEYFILE_KEY = 'dchain_keyfile';
+const CONTACTS_KEY = 'dchain_contacts';
+const SETTINGS_KEY = 'dchain_settings';
+const CHATS_KEY = 'dchain_chats';
+
+/** Save the key file in secure storage (encrypted on device). */
+export async function saveKeyFile(kf: KeyFile): Promise<void> {
+  await SecureStore.setItemAsync(KEYFILE_KEY, JSON.stringify(kf));
+}
+
+/** Load key file. Returns null if not set. */
+export async function loadKeyFile(): Promise<KeyFile | null> {
+  const raw = await SecureStore.getItemAsync(KEYFILE_KEY);
+  if (!raw) return null;
+  return JSON.parse(raw) as KeyFile;
+}
+
+/** Delete key file (logout / factory reset). */
+export async function deleteKeyFile(): Promise<void> {
+  await SecureStore.deleteItemAsync(KEYFILE_KEY);
+}
+
+// ─── Node settings ─────────────────────────────────────────────────────────────
+
+const DEFAULT_SETTINGS: NodeSettings = {
+  nodeUrl:    'http://localhost:8081',
+  contractId: '',
+};
+
+export async function loadSettings(): Promise<NodeSettings> {
+  const raw = await AsyncStorage.getItem(SETTINGS_KEY);
+  if (!raw) return DEFAULT_SETTINGS;
+  return { ...DEFAULT_SETTINGS, ...JSON.parse(raw) };
+}
+
+export async function saveSettings(s: Partial<NodeSettings>): Promise<void> {
+  const current = await loadSettings();
+  await AsyncStorage.setItem(SETTINGS_KEY, JSON.stringify({ ...current, ...s }));
+}
+
+// ─── Contacts ─────────────────────────────────────────────────────────────────
+
+export async function loadContacts(): Promise<Contact[]> {
+  const raw = await AsyncStorage.getItem(CONTACTS_KEY);
+  if (!raw) return [];
+  return JSON.parse(raw) as Contact[];
+}
+
+export async function saveContact(c: Contact): Promise<void> {
+  const contacts = await loadContacts();
+  const idx = contacts.findIndex(x => x.address === c.address);
+  if (idx >= 0) contacts[idx] = c;
+  else contacts.push(c);
+  await AsyncStorage.setItem(CONTACTS_KEY, JSON.stringify(contacts));
+}
+
+export async function deleteContact(address: string): Promise<void> {
+  const contacts = await loadContacts();
+  await AsyncStorage.setItem(
+    CONTACTS_KEY,
+    JSON.stringify(contacts.filter(c => c.address !== address)),
+  );
+}
+
+// ─── Message cache (per-chat local store) ────────────────────────────────────
+
+export interface CachedMessage {
+  id:        string;
+  from:      string;
+  text:      string;
+  timestamp: number;
+  mine:      boolean;
+}
+
+export async function loadMessages(chatId: string): Promise<CachedMessage[]> {
+  const raw = await AsyncStorage.getItem(`${CHATS_KEY}_${chatId}`);
+  if (!raw) return [];
+  return JSON.parse(raw) as CachedMessage[];
+}
+
+export async function appendMessage(chatId: string, msg: CachedMessage): Promise<void> {
+  const msgs = await loadMessages(chatId);
+  // Deduplicate by id
+  if (msgs.find(m => m.id === msg.id)) return;
+  msgs.push(msg);
+  // Keep last 500 messages per chat
+  const trimmed = msgs.slice(-500);
+  await AsyncStorage.setItem(`${CHATS_KEY}_${chatId}`, JSON.stringify(trimmed));
+}