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

node/version/version.go

@@ -0,0 +1,70 @@
+// Package version carries build-time identity for the node binary.
+//
+// All four variables below are overridable at link time via -ldflags -X. The
+// canonical build command is:
+//
+//	VERSION_TAG=$(git describe --tags --always --dirty)
+//	VERSION_COMMIT=$(git rev-parse HEAD)
+//	VERSION_DATE=$(date -u +%Y-%m-%dT%H:%M:%SZ)
+//	VERSION_DIRTY=$(git diff --quiet HEAD -- 2>/dev/null && echo false || echo true)
+//
+//	go build -ldflags "\
+//	  -X go-blockchain/node/version.Tag=$VERSION_TAG \
+//	  -X go-blockchain/node/version.Commit=$VERSION_COMMIT \
+//	  -X go-blockchain/node/version.Date=$VERSION_DATE \
+//	  -X go-blockchain/node/version.Dirty=$VERSION_DIRTY" ./cmd/node
+//
+// Both Dockerfile and Dockerfile.slim run this at image build time (see ARG
+// VERSION_* + RUN go build … -ldflags lines). A naked `go build ./...`
+// without ldflags falls back to the zero defaults — that's fine for local
+// dev, just not shipped to users.
+//
+// Protocol versions come from a different source: see node.ProtocolVersion,
+// which is a compile-time const that only bumps on wire-protocol breaking
+// changes. Protocol version can be the same across many build tags.
+package version
+
+// Tag is a human-readable version label, typically `git describe --tags
+// --always --dirty`. Examples: "v0.5.1", "v0.5.1-3-gabc1234", "abc1234-dirty".
+// "dev" is the fallback when built without ldflags.
+var Tag = "dev"
+
+// Commit is the full 40-char git SHA of the HEAD at build time. "none" when
+// unset. Useful for precise bisect / release-channel lookups even when Tag
+// is a non-unique label like "dev".
+var Commit = "none"
+
+// Date is the build timestamp in RFC3339 (UTC). "unknown" when unset.
+// Exposed in /api/well-known-version so operators can see how stale a
+// deployed binary is without `docker exec`.
+var Date = "unknown"
+
+// Dirty is the string "true" if the working tree had uncommitted changes at
+// build time, "false" otherwise. Always a string (not bool) because ldflags
+// can only inject strings — parse with == "true" at call sites.
+var Dirty = "false"
+
+// String returns a one-line summary suitable for `node --version` output.
+// Format: "dchain-node <tag> (commit=<short> date=<date> dirty=<bool>)".
+func String() string {
+	short := Commit
+	if len(short) > 8 {
+		short = short[:8]
+	}
+	return "dchain-node " + Tag + " (commit=" + short + " date=" + Date + " dirty=" + Dirty + ")"
+}
+
+// Info returns the version fields as a map, suitable for JSON embedding in
+// /api/well-known-version and similar introspection endpoints.
+func Info() map[string]string {
+	return map[string]string{
+		"tag":    Tag,
+		"commit": Commit,
+		"date":   Date,
+		"dirty":  Dirty,
+	}
+}
+
+// IsDirty reports whether the build was from an unclean working tree.
+// Convenience over parsing Dirty == "true" at call sites.
+func IsDirty() bool { return Dirty == "true" }