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/components/ui/Button.tsx

@@ -0,0 +1,76 @@
+import React from 'react';
+import { Pressable, Text, ActivityIndicator } from 'react-native';
+import { cva, type VariantProps } from 'class-variance-authority';
+import { cn } from '@/lib/utils';
+
+const buttonVariants = cva(
+  'flex-row items-center justify-center rounded-xl px-5 py-3 active:opacity-80',
+  {
+    variants: {
+      variant: {
+        default:     'bg-primary',
+        secondary:   'bg-surfaceHigh border border-border',
+        destructive: 'bg-destructive',
+        ghost:       'bg-transparent',
+        outline:     'bg-transparent border border-primary',
+      },
+      size: {
+        sm:   'px-3 py-2',
+        md:   'px-5 py-3',
+        lg:   'px-6 py-4',
+        icon: 'p-2',
+      },
+    },
+    defaultVariants: {
+      variant: 'default',
+      size:    'md',
+    },
+  },
+);
+
+const textVariants = cva('font-semibold text-center', {
+  variants: {
+    variant: {
+      default:     'text-white',
+      secondary:   'text-white',
+      destructive: 'text-white',
+      ghost:       'text-primary',
+      outline:     'text-primary',
+    },
+    size: {
+      sm:   'text-sm',
+      md:   'text-base',
+      lg:   'text-lg',
+      icon: 'text-base',
+    },
+  },
+  defaultVariants: {
+    variant: 'default',
+    size:    'md',
+  },
+});
+
+interface ButtonProps extends VariantProps<typeof buttonVariants> {
+  onPress?:   () => void;
+  disabled?:  boolean;
+  loading?:   boolean;
+  children:   React.ReactNode;
+  className?: string;
+}
+
+export function Button({
+  variant, size, onPress, disabled, loading, children, className,
+}: ButtonProps) {
+  return (
+    <Pressable
+      onPress={onPress}
+      disabled={disabled || loading}
+      className={cn(buttonVariants({ variant, size }), disabled && 'opacity-50', className)}
+    >
+      {loading
+        ? <ActivityIndicator color="#fff" size="small" />
+        : <Text className={textVariants({ variant, size })}>{children}</Text>
+      }
+    </Pressable>
+  );
+}