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/app/(app)/_layout.tsx

@@ -0,0 +1,127 @@
+/**
+ * Main app tab layout.
+ * Redirects to welcome if no key found.
+ */
+
+import React, { useEffect } from 'react';
+import { Tabs, router } from 'expo-router';
+import { Ionicons } from '@expo/vector-icons';
+import { useSafeAreaInsets } from 'react-native-safe-area-context';
+import { useStore } from '@/lib/store';
+import { useBalance } from '@/hooks/useBalance';
+import { useContacts } from '@/hooks/useContacts';
+import { useWellKnownContracts } from '@/hooks/useWellKnownContracts';
+import { getWSClient } from '@/lib/ws';
+
+const C_ACCENT = '#7db5ff';
+const C_MUTED  = '#98a7c2';
+const C_BG     = '#111a2b';
+const C_BORDER = '#1c2840';
+
+export default function AppLayout() {
+  const keyFile  = useStore(s => s.keyFile);
+  const requests = useStore(s => s.requests);
+  const insets   = useSafeAreaInsets();
+
+  useBalance();
+  useContacts();
+  useWellKnownContracts();  // auto-discover canonical system contracts from node
+
+  // Arm the WS client with this user's Ed25519 keypair. The client signs the
+  // server's auth nonce on every (re)connect so scoped subscriptions
+  // (addr:<my_pub>, inbox:<my_x25519>) are accepted. Without this the
+  // server would still accept global topic subs but reject scoped ones.
+  useEffect(() => {
+    const ws = getWSClient();
+    if (keyFile) {
+      ws.setAuthCreds({ pubKey: keyFile.pub_key, privKey: keyFile.priv_key });
+    } else {
+      ws.setAuthCreds(null);
+    }
+  }, [keyFile]);
+
+  useEffect(() => {
+    if (keyFile === null) {
+      const t = setTimeout(() => {
+        if (!useStore.getState().keyFile) router.replace('/');
+      }, 300);
+      return () => clearTimeout(t);
+    }
+  }, [keyFile]);
+
+  // Tab bar layout math:
+  //   icon (22) + gap (4) + label (~13) = ~39px of content
+  //   We add a 12px visual margin above, and pad the bottom by the larger of
+  //   the platform safe-area inset or 10px so the bar never sits flush on the
+  //   home indicator.
+  const BAR_CONTENT_HEIGHT = 52;
+  const bottomPad          = Math.max(insets.bottom, 10);
+
+  return (
+    <Tabs
+      screenOptions={{
+        headerShown:             false,
+        tabBarActiveTintColor:   C_ACCENT,
+        tabBarInactiveTintColor: C_MUTED,
+        tabBarLabelStyle: {
+          fontSize:    10,
+          fontWeight:  '500',
+          marginTop:   2,
+        },
+        tabBarStyle: {
+          backgroundColor: C_BG,
+          borderTopColor:  C_BORDER,
+          borderTopWidth:  1,
+          height:          BAR_CONTENT_HEIGHT + bottomPad,
+          paddingTop:      8,
+          paddingBottom:   bottomPad,
+        },
+      }}
+    >
+      <Tabs.Screen
+        name="chats"
+        options={{
+          tabBarLabel: 'Чаты',
+          tabBarIcon: ({ color, focused }) => (
+            <Ionicons
+              name={focused ? 'chatbubbles' : 'chatbubbles-outline'}
+              size={22}
+              color={color}
+            />
+          ),
+          tabBarBadge:      requests.length > 0 ? requests.length : undefined,
+          tabBarBadgeStyle: { backgroundColor: C_ACCENT, fontSize: 10 },
+        }}
+      />
+      <Tabs.Screen
+        name="wallet"
+        options={{
+          tabBarLabel: 'Кошелёк',
+          tabBarIcon: ({ color, focused }) => (
+            <Ionicons
+              name={focused ? 'wallet' : 'wallet-outline'}
+              size={22}
+              color={color}
+            />
+          ),
+        }}
+      />
+      <Tabs.Screen
+        name="settings"
+        options={{
+          tabBarLabel: 'Настройки',
+          tabBarIcon: ({ color, focused }) => (
+            <Ionicons
+              name={focused ? 'settings' : 'settings-outline'}
+              size={22}
+              color={color}
+            />
+          ),
+        }}
+      />
+      {/* Non-tab screens — hidden from tab bar */}
+      <Tabs.Screen name="requests"    options={{ href: null }} />
+      <Tabs.Screen name="new-contact" options={{ href: null }} />
+    </Tabs>
+  );
+}