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

contracts/username_registry/username_registry_abi.json

@@ -0,0 +1,50 @@
+{
+  "contract": "username_registry",
+  "version": "1.0.0",
+  "description": "Maps human-readable usernames to wallet addresses. Shorter names cost more to register. Fees go to the contract treasury.",
+  "methods": [
+    {
+      "name": "register",
+      "description": "Register a username for the caller. Fee = 10^(7 - min(len,6)) µT (1-char=10M, 2=1M, 3=100K, 4=10K, 5=1K, 6+=100). Caller must have sufficient balance.",
+      "args": [
+        {"name": "name", "type": "string", "description": "Username to register (max 64 chars, lowercase)"}
+      ]
+    },
+    {
+      "name": "resolve",
+      "description": "Look up the wallet address that owns a username. Logs 'owner: <address>' or 'not found: <name>'.",
+      "args": [
+        {"name": "name", "type": "string", "description": "Username to look up"}
+      ]
+    },
+    {
+      "name": "lookup",
+      "description": "Reverse lookup: find the username registered to a given address. Logs 'name: <username>' or 'no name: <address>'.",
+      "args": [
+        {"name": "address", "type": "string", "description": "Wallet address (hex pubkey)"}
+      ]
+    },
+    {
+      "name": "transfer",
+      "description": "Transfer ownership of a username to another address. Only the current owner may call this.",
+      "args": [
+        {"name": "name", "type": "string", "description": "Username to transfer"},
+        {"name": "new_owner", "type": "string", "description": "New owner address (hex pubkey)"}
+      ]
+    },
+    {
+      "name": "release",
+      "description": "Release a username registration. Only the current owner may call this.",
+      "args": [
+        {"name": "name", "type": "string", "description": "Username to release"}
+      ]
+    },
+    {
+      "name": "fee",
+      "description": "Query the registration fee for a given name length. Logs 'fee: <amount>' in µT.",
+      "args": [
+        {"name": "name", "type": "string", "description": "Name whose fee you want to check"}
+      ]
+    }
+  ]
+}