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/api_channels.go

@@ -0,0 +1,102 @@
+// Package node — channel endpoints.
+//
+// `/api/channels/:id/members` returns every Ed25519 pubkey registered as a
+// channel member together with their current X25519 pubkey (from the
+// identity registry). Clients sealing a message to a channel iterate this
+// list and call relay.Seal once per recipient — that's the "fan-out"
+// group-messaging model (R1 in the roadmap).
+//
+// Why enrich with X25519 here rather than making the client do it?
+//   - One HTTP round trip vs N. At 10+ members the latency difference is
+//     significant over mobile networks.
+//   - The server already holds the identity state; no extra DB hops.
+//   - Clients get a stable, already-joined view — if a member hasn't
+//     published an X25519 key yet, we return them with `x25519_pub_key=""`
+//     so the caller knows to skip or retry later.
+package node
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+
+	"go-blockchain/blockchain"
+	"go-blockchain/wallet"
+)
+
+func registerChannelAPI(mux *http.ServeMux, q ExplorerQuery) {
+	// GET /api/channels/{id}              → channel metadata
+	// GET /api/channels/{id}/members      → enriched member list
+	//
+	// One HandleFunc deals with both by sniffing the path suffix.
+	mux.HandleFunc("/api/channels/", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			jsonErr(w, fmt.Errorf("method not allowed"), 405)
+			return
+		}
+		path := strings.TrimPrefix(r.URL.Path, "/api/channels/")
+		path = strings.Trim(path, "/")
+		if path == "" {
+			jsonErr(w, fmt.Errorf("channel id required"), 400)
+			return
+		}
+		switch {
+		case strings.HasSuffix(path, "/members"):
+			id := strings.TrimSuffix(path, "/members")
+			handleChannelMembers(w, q, id)
+		default:
+			handleChannelInfo(w, q, path)
+		}
+	})
+}
+
+func handleChannelInfo(w http.ResponseWriter, q ExplorerQuery, channelID string) {
+	if q.GetChannel == nil {
+		jsonErr(w, fmt.Errorf("channel queries not configured"), 503)
+		return
+	}
+	ch, err := q.GetChannel(channelID)
+	if err != nil {
+		jsonErr(w, err, 500)
+		return
+	}
+	if ch == nil {
+		jsonErr(w, fmt.Errorf("channel %s not found", channelID), 404)
+		return
+	}
+	jsonOK(w, ch)
+}
+
+func handleChannelMembers(w http.ResponseWriter, q ExplorerQuery, channelID string) {
+	if q.GetChannelMembers == nil {
+		jsonErr(w, fmt.Errorf("channel queries not configured"), 503)
+		return
+	}
+	pubs, err := q.GetChannelMembers(channelID)
+	if err != nil {
+		jsonErr(w, err, 500)
+		return
+	}
+	out := make([]blockchain.ChannelMember, 0, len(pubs))
+	for _, pub := range pubs {
+		member := blockchain.ChannelMember{
+			PubKey:  pub,
+			Address: wallet.PubKeyToAddress(pub),
+		}
+		// Best-effort X25519 lookup — skip silently on miss so a member
+		// who hasn't published their identity yet doesn't prevent the
+		// whole list from returning. The sender will just skip them on
+		// fan-out and retry later (after that member does register).
+		if q.IdentityInfo != nil {
+			if info, err := q.IdentityInfo(pub); err == nil && info != nil {
+				member.X25519PubKey = info.X25519Pub
+			}
+		}
+		out = append(out, member)
+	}
+	jsonOK(w, map[string]any{
+		"channel_id": channelID,
+		"count":      len(out),
+		"members":    out,
+	})
+}