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/crypto.ts

@@ -0,0 +1,168 @@
+/**
+ * Cryptographic operations for DChain messenger.
+ *
+ * Ed25519  — transaction signing (via TweetNaCl sign)
+ * X25519   — Diffie-Hellman key exchange for NaCl box
+ * NaCl box — authenticated encryption for relay messages
+ */
+
+import nacl from 'tweetnacl';
+import { decodeUTF8, encodeUTF8 } from 'tweetnacl-util';
+import { getRandomBytes } from 'expo-crypto';
+import type { KeyFile } from './types';
+
+// ─── PRNG ─────────────────────────────────────────────────────────────────────
+// TweetNaCl looks for window.crypto which doesn't exist in React Native/Hermes.
+// Wire nacl to expo-crypto which uses the platform's secure RNG natively.
+nacl.setPRNG((output: Uint8Array, length: number) => {
+  const bytes = getRandomBytes(length);
+  for (let i = 0; i < length; i++) output[i] = bytes[i];
+});
+
+// ─── Helpers ──────────────────────────────────────────────────────────────────
+
+export function hexToBytes(hex: string): Uint8Array {
+  if (hex.length % 2 !== 0) throw new Error('odd hex length');
+  const bytes = new Uint8Array(hex.length / 2);
+  for (let i = 0; i < bytes.length; i++) {
+    bytes[i] = parseInt(hex.slice(i * 2, i * 2 + 2), 16);
+  }
+  return bytes;
+}
+
+export function bytesToHex(bytes: Uint8Array): string {
+  return Array.from(bytes).map(b => b.toString(16).padStart(2, '0')).join('');
+}
+
+// ─── Key generation ───────────────────────────────────────────────────────────
+
+/**
+ * Generate a new identity: Ed25519 signing keys + X25519 encryption keys.
+ * Returns a KeyFile compatible with the Go node format.
+ */
+export function generateKeyFile(): KeyFile {
+  // Ed25519 for signing / blockchain identity
+  const signKP = nacl.sign.keyPair();
+
+  // X25519 for NaCl box encryption
+  // nacl.box.keyPair() returns Curve25519 keys
+  const boxKP = nacl.box.keyPair();
+
+  return {
+    pub_key:     bytesToHex(signKP.publicKey),
+    priv_key:    bytesToHex(signKP.secretKey),
+    x25519_pub:  bytesToHex(boxKP.publicKey),
+    x25519_priv: bytesToHex(boxKP.secretKey),
+  };
+}
+
+// ─── NaCl box encryption ──────────────────────────────────────────────────────
+
+/**
+ * Encrypt a plaintext message using NaCl box.
+ * Sender uses their X25519 secret key + recipient's X25519 public key.
+ * Returns { nonce, ciphertext } as hex strings.
+ */
+export function encryptMessage(
+  plaintext:        string,
+  senderSecretHex:  string,
+  recipientPubHex:  string,
+): { nonce: string; ciphertext: string } {
+  const nonce      = nacl.randomBytes(nacl.box.nonceLength);
+  const message    = decodeUTF8(plaintext);
+  const secretKey  = hexToBytes(senderSecretHex);
+  const publicKey  = hexToBytes(recipientPubHex);
+
+  const box = nacl.box(message, nonce, publicKey, secretKey);
+  return {
+    nonce:      bytesToHex(nonce),
+    ciphertext: bytesToHex(box),
+  };
+}
+
+/**
+ * Decrypt a NaCl box.
+ * Recipient uses their X25519 secret key + sender's X25519 public key.
+ */
+export function decryptMessage(
+  ciphertextHex:    string,
+  nonceHex:         string,
+  senderPubHex:     string,
+  recipientSecHex:  string,
+): string | null {
+  try {
+    const ciphertext = hexToBytes(ciphertextHex);
+    const nonce      = hexToBytes(nonceHex);
+    const senderPub  = hexToBytes(senderPubHex);
+    const secretKey  = hexToBytes(recipientSecHex);
+
+    const plain = nacl.box.open(ciphertext, nonce, senderPub, secretKey);
+    if (!plain) return null;
+    return encodeUTF8(plain);
+  } catch {
+    return null;
+  }
+}
+
+// ─── Ed25519 signing ──────────────────────────────────────────────────────────
+
+/**
+ * Sign arbitrary data with the Ed25519 private key.
+ * Returns signature as hex.
+ */
+export function sign(data: Uint8Array, privKeyHex: string): string {
+  const secretKey = hexToBytes(privKeyHex);
+  const sig = nacl.sign.detached(data, secretKey);
+  return bytesToHex(sig);
+}
+
+/**
+ * Sign arbitrary data with the Ed25519 private key.
+ * Returns signature as base64 — this is the format the Go blockchain node
+ * expects ([]byte fields are base64 in JSON).
+ */
+export function signBase64(data: Uint8Array, privKeyHex: string): string {
+  const secretKey = hexToBytes(privKeyHex);
+  const sig = nacl.sign.detached(data, secretKey);
+  return bytesToBase64(sig);
+}
+
+/** Encode bytes as base64. Works on Hermes (btoa is available since RN 0.71). */
+export function bytesToBase64(bytes: Uint8Array): string {
+  let binary = '';
+  for (let i = 0; i < bytes.length; i++) {
+    binary += String.fromCharCode(bytes[i]);
+  }
+  return btoa(binary);
+}
+
+/**
+ * Decode base64 → bytes. Accepts both standard and URL-safe variants (the
+ * node's /relay/inbox returns `[]byte` fields marshalled via Go's default
+ * json.Marshal which uses standard base64).
+ */
+export function base64ToBytes(b64: string): Uint8Array {
+  const binary = atob(b64.replace(/-/g, '+').replace(/_/g, '/'));
+  const out = new Uint8Array(binary.length);
+  for (let i = 0; i < binary.length; i++) out[i] = binary.charCodeAt(i);
+  return out;
+}
+
+/**
+ * Verify an Ed25519 signature.
+ */
+export function verify(data: Uint8Array, sigHex: string, pubKeyHex: string): boolean {
+  try {
+    return nacl.sign.detached.verify(data, hexToBytes(sigHex), hexToBytes(pubKeyHex));
+  } catch {
+    return false;
+  }
+}
+
+// ─── Address helpers ──────────────────────────────────────────────────────────
+
+/** Truncate a long hex address for display: 8...8 */
+export function shortAddr(hex: string, chars = 8): string {
+  if (hex.length <= chars * 2 + 3) return hex;
+  return `${hex.slice(0, chars)}…${hex.slice(-chars)}`;
+}