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

deploy/single/systemd/README.md

@@ -0,0 +1,57 @@
+# Systemd units for DChain auto-update
+
+Two files, one-time setup.
+
+## Install
+
+Assumes the repo is checked out at `/opt/dchain`. Adjust `WorkingDirectory=`
+and `EnvironmentFile=` in `dchain-update.service` if you put it elsewhere.
+
+```bash
+sudo cp dchain-update.{service,timer} /etc/systemd/system/
+sudo systemctl daemon-reload
+sudo systemctl enable --now dchain-update.timer
+```
+
+## Verify
+
+```bash
+# When does the timer next fire?
+systemctl list-timers dchain-update.timer
+
+# What did the last run do?
+journalctl -u dchain-update.service -n 100 --no-pager
+
+# Run one update immediately, without waiting for the timer
+sudo systemctl start dchain-update.service
+```
+
+## How it behaves
+
+- Every hour (± up to 15 min jitter) the timer triggers the service.
+- The service runs `update.sh` once, which:
+  - fetches `origin/main`
+  - if HEAD didn't move: exits 0, nothing touched
+  - if HEAD moved: fast-forwards, rebuilds image, smoke-tests the new
+    binary, restarts the container, polls health
+- Downtime per update is ~5-8 seconds (Badger reopen + HTTP listener warm-up).
+- Failures write to journal; add `OnFailure=` if you want Pushover/email.
+
+## Disable auto-update
+
+If you want to pin a version and review changes manually:
+
+```bash
+sudo systemctl disable --now dchain-update.timer
+```
+
+You can still invoke `update.sh` by hand when you've reviewed and
+fast-forwarded your working tree.
+
+## Why hourly + jitter
+
+A whole federation restarting in the same 60-second window would drop PBFT
+quorum below 2/3 for that window. With 1-hour cadence and 15-min jitter, the
+max probability of two validators being down simultaneously is about
+`(15s / 15min)² × N_validators²`, which stays safely below the quorum floor
+for any realistic N.

deploy/single/systemd/dchain-update.service

@@ -0,0 +1,35 @@
+# DChain single-node pull-and-restart service.
+#
+# Install:
+#   sudo cp dchain-update.service dchain-update.timer /etc/systemd/system/
+#   sudo systemctl daemon-reload
+#   sudo systemctl enable --now dchain-update.timer
+#
+# View runs:
+#   systemctl list-timers dchain-update.timer
+#   journalctl -u dchain-update.service -n 200 --no-pager
+#
+# The timer (sibling file) fires the service; the service runs update.sh
+# once per fire, which itself is a no-op when HEAD hasn't moved.
+
+[Unit]
+Description=DChain node: fetch latest, rebuild, rolling restart
+Documentation=file:///opt/dchain/deploy/UPDATE_STRATEGY.md
+# Don't try to update while Docker is still coming up after a host reboot.
+After=docker.service network-online.target
+Requires=docker.service
+
+[Service]
+Type=oneshot
+# REPO_DIR + COMPOSE_FILE come from the update script's defaults; override
+# here with Environment= if you moved the checkout to a non-default path.
+WorkingDirectory=/opt/dchain
+EnvironmentFile=-/opt/dchain/deploy/single/node.env
+ExecStart=/opt/dchain/deploy/single/update.sh
+
+# Lock down the unit — update.sh only needs git + docker + curl.
+PrivateTmp=true
+NoNewPrivileges=true
+ProtectSystem=strict
+ReadWritePaths=/opt/dchain /var/run/docker.sock
+ProtectHome=true

deploy/single/systemd/dchain-update.timer

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+# Timer for dchain-update.service — fires hourly with a random 15-minute jitter.
+#
+# Why the jitter: if every operator on the same network runs `OnCalendar=hourly`
+# at :00:00, the whole federation restarts its nodes in the same minute and
+# PBFT quorum drops below 2/3. With a random delay spread across 15 minutes
+# each node updates at a slightly different time, so at any instant the vast
+# majority of validators remain live.
+#
+# Persistent=true means if the machine was asleep/off at fire time, the timer
+# catches up on next boot instead of silently skipping.
+
+[Unit]
+Description=Run DChain node update hourly
+Requires=dchain-update.service
+
+[Timer]
+OnBootSec=10min
+OnUnitActiveSec=1h
+RandomizedDelaySec=15min
+Persistent=true
+Unit=dchain-update.service
+
+[Install]
+WantedBy=timers.target