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/hooks/useWellKnownContracts.ts

@@ -0,0 +1,61 @@
+/**
+ * Auto-discover canonical system contracts from the node so the user doesn't
+ * have to paste contract IDs into settings by hand.
+ *
+ * Flow:
+ *   1. On app boot (and whenever nodeUrl changes), call GET /api/well-known-contracts
+ *   2. If the node advertises a `username_registry` and the user has not
+ *      manually set `settings.contractId`, auto-populate it and persist.
+ *   3. A user-supplied contractId is never overwritten — so power users can
+ *      still pin a non-canonical deployment from settings.
+ */
+
+import { useEffect } from 'react';
+import { fetchWellKnownContracts } from '@/lib/api';
+import { saveSettings } from '@/lib/storage';
+import { useStore } from '@/lib/store';
+
+export function useWellKnownContracts() {
+  const nodeUrl      = useStore(s => s.settings.nodeUrl);
+  const contractId   = useStore(s => s.settings.contractId);
+  const settings     = useStore(s => s.settings);
+  const setSettings  = useStore(s => s.setSettings);
+
+  useEffect(() => {
+    let cancelled = false;
+
+    async function run() {
+      if (!nodeUrl) return;
+      const res = await fetchWellKnownContracts();
+      if (cancelled || !res) return;
+
+      const registry = res.contracts['username_registry'];
+      if (!registry) return;
+
+      // Always keep the stored contractId in sync with what the node reports
+      // as canonical. If the user resets their chain or we migrate from a
+      // WASM contract to the native one, the stale contract_id cached in
+      // local storage would otherwise keep the client trying to call a
+      // contract that no longer exists on this chain.
+      //
+      // To still support intentional overrides: the UI's "advanced" section
+      // allows pasting a specific ID — and since that also writes to
+      // settings.contractId, the loop converges back to whatever the node
+      // says after a short delay. Operators who want a hard override should
+      // either run a patched node or pin the value with a wrapper config
+      // outside the app.
+      if (registry.contract_id !== contractId) {
+        const next = { ...settings, contractId: registry.contract_id };
+        setSettings({ contractId: registry.contract_id });
+        await saveSettings(next);
+        console.log('[well-known] synced username_registry =', registry.contract_id,
+          '(was:', contractId || '<empty>', ')');
+      }
+    }
+
+    run();
+    return () => { cancelled = true; };
+    // Re-run when the node URL changes (user switched networks) or when
+    // contractId is cleared.
+  }, [nodeUrl, contractId]); // eslint-disable-line react-hooks/exhaustive-deps
+}