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/components/Header.tsx

@@ -0,0 +1,76 @@
+/**
+ * Header — единая шапка экрана: [left slot] [title centered] [right slot].
+ *
+ * Правила выравнивания:
+ *   - left/right принимают натуральную ширину контента (обычно 1-2
+ *     IconButton'а 36px, или pressable-avatar 32px).
+ *   - title (ReactNode, принимает как string, так и compound — аватар +
+ *     имя вместе) всегда центрирован через flex:1 + alignItems:center.
+ *     Абсолютно не позиционируется, т.к. при слишком широком title'е
+ *     лучше ужать его, чем наложить на кнопки.
+ *
+ * `title` может быть строкой (тогда рендерится как Text 17px semibold)
+ * либо произвольным node'ом — используется в chat detail для
+ * [avatar][name + typing-subtitle] compound-блока.
+ *
+ * `divider` (default true) — тонкая 1px линия снизу; в tab-страницах
+ * обычно выключена (TabHeader всегда ставит divider=false).
+ */
+import React, { ReactNode } from 'react';
+import { View, Text } from 'react-native';
+
+export interface HeaderProps {
+  title?: ReactNode;
+  left?:  ReactNode;
+  right?: ReactNode;
+  /** Показывать нижнюю тонкую линию-разделитель. По умолчанию true. */
+  divider?: boolean;
+}
+
+export function Header({ title, left, right, divider = true }: HeaderProps) {
+  return (
+    <View
+      style={{
+        paddingHorizontal: 14,
+        paddingVertical: 10,
+        borderBottomWidth: divider ? 1 : 0,
+        borderBottomColor: '#0f0f0f',
+      }}
+    >
+      <View
+        style={{
+          flexDirection: 'row',
+          alignItems: 'center',
+          minHeight: 44,
+        }}
+      >
+        {/* Left slot — натуральная ширина, минимум 44 чтобы title
+            визуально центрировался для одно-icon-left + одно-icon-right. */}
+        <View style={{ minWidth: 44, alignItems: 'flex-start' }}>{left}</View>
+
+        {/* Title centered */}
+        <View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}>
+          {typeof title === 'string' ? (
+            <Text
+              numberOfLines={1}
+              style={{
+                color: '#ffffff',
+                fontSize: 17,
+                fontWeight: '700',
+                letterSpacing: -0.2,
+              }}
+            >
+              {title}
+            </Text>
+          ) : title ?? null}
+        </View>
+
+        {/* Right slot — row, натуральная ширина, минимум 44. gap=4
+            чтобы несколько IconButton'ов не слипались в selection-mode. */}
+        <View style={{ minWidth: 44, flexDirection: 'row', justifyContent: 'flex-end', gap: 4 }}>
+          {right}
+        </View>
+      </View>
+    </View>
+  );
+}