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/sdk/dchain_stub.go

@@ -0,0 +1,53 @@
+//go:build !tinygo
+
+// Package dchain provides stub implementations for non-TinyGo builds.
+// These allow go build / IDEs to compile contract code without TinyGo.
+// The stubs panic at runtime — they are never executed in production.
+package dchain
+
+// ArgStr returns the idx-th call argument as a string.
+func ArgStr(idx int, maxLen int) string { panic("dchain: ArgStr requires TinyGo (tinygo build -target wasip1)") }
+
+// ArgU64 returns the idx-th call argument as a uint64.
+func ArgU64(idx int) uint64 { panic("dchain: ArgU64 requires TinyGo") }
+
+// GetState reads a value from contract state.
+func GetState(key string) []byte { panic("dchain: GetState requires TinyGo") }
+
+// GetStateStr reads a contract state value as a string.
+func GetStateStr(key string) string { panic("dchain: GetStateStr requires TinyGo") }
+
+// SetState writes a value to contract state.
+func SetState(key string, value []byte) { panic("dchain: SetState requires TinyGo") }
+
+// SetStateStr writes a string value to contract state.
+func SetStateStr(key, value string) { panic("dchain: SetStateStr requires TinyGo") }
+
+// GetU64 reads a uint64 from contract state.
+func GetU64(key string) uint64 { panic("dchain: GetU64 requires TinyGo") }
+
+// PutU64 stores a uint64 in contract state.
+func PutU64(key string, val uint64) { panic("dchain: PutU64 requires TinyGo") }
+
+// Caller returns the hex pubkey of the transaction sender.
+func Caller() string { panic("dchain: Caller requires TinyGo") }
+
+// BlockHeight returns the current block height.
+func BlockHeight() uint64 { panic("dchain: BlockHeight requires TinyGo") }
+
+// Treasury returns the contract's ownerless treasury address.
+func Treasury() string { panic("dchain: Treasury requires TinyGo") }
+
+// Balance returns the token balance of a hex pubkey in µT.
+func Balance(pubKey string) uint64 { panic("dchain: Balance requires TinyGo") }
+
+// Transfer sends amount µT from one address to another.
+func Transfer(from, to string, amount uint64) bool { panic("dchain: Transfer requires TinyGo") }
+
+// CallContract executes a method on another deployed contract.
+func CallContract(contractID, method, argsJSON string) bool {
+	panic("dchain: CallContract requires TinyGo")
+}
+
+// Log writes a message to the contract log.
+func Log(msg string) { panic("dchain: Log requires TinyGo") }