chore: initial commit for v0.0.1

DChain single-node blockchain + React Native messenger client.

Core:
- PBFT consensus with multi-sig validator admission + equivocation slashing
- BadgerDB + schema migration scaffold (CurrentSchemaVersion=0)
- libp2p gossipsub (tx/v1, blocks/v1, relay/v1, version/v1)
- Native Go contracts (username_registry) alongside WASM (wazero)
- WebSocket gateway with topic-based fanout + Ed25519-nonce auth
- Relay mailbox with NaCl envelope encryption (X25519 + Ed25519)
- Prometheus /metrics, per-IP rate limit, body-size cap

Deployment:
- Single-node compose (deploy/single/) with Caddy TLS + optional Prometheus
- 3-node dev compose (docker-compose.yml) with mocked internet topology
- 3-validator prod compose (deploy/prod/) for federation
- Auto-update from Gitea via /api/update-check + systemd timer
- Build-time version injection (ldflags → node --version)
- UI / Swagger toggle flags (DCHAIN_DISABLE_UI, DCHAIN_DISABLE_SWAGGER)

Client (client-app/):
- Expo / React Native / NativeWind
- E2E NaCl encryption, typing indicator, contact requests
- Auto-discovery of canonical contracts, chain_id aware, WS reconnect on node switch

Documentation:
- README.md, CHANGELOG.md, CONTEXT.md
- deploy/single/README.md with 6 operator scenarios
- deploy/UPDATE_STRATEGY.md with 4-layer forward-compat design
- docs/contracts/*.md per contract

client-app/lib/crypto.ts

@@ -0,0 +1,156 @@
+/**
+ * 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);
+}
+
+/**
+ * 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)}`;
+}