feat: single-node Zopu runtime deployment for Debian

Lane D deliverable: reproducible execution-plane deployment on a fresh
Debian dedicated server (~12 cores, 40 GB RAM, single-node).

Artifacts:
- bootstrap.sh: Docker Engine, Bun, repo clone, build, systemd install,
  firewall (deny-by-default), optional Tailscale, disk monitor cron
- .env.template: all 8 environment groups documented (Convex, Gitea,
  model gateway, AgentOS/RivetKit, Zopu agent, daemon, Docker sandbox,
  service auth)
- systemd units: zopu-daemon, zopu-agent (both Restart=always),
  zopu-health timer (60s), zopu-docker-cleanup timer (daily)
- scripts: health-check, update, rollback, docker-cleanup, disk-monitor
- Caddyfile: optional reverse proxy (documentation-only by default)
- README.md: full runbook with start/stop/log/update/rollback/cleanup
  procedures, topology documentation, and boundary notes

Verified topology (from installed RivetKit source):
- registry.start() boots an in-process RivetKit engine (envoy mode) with
  a native Rust sidecar at http://localhost:6420 (DEFAULT_ENDPOINT in
  chunk-YDUQHING.js line 4751). createClient() connects back to it.
- No separate Rivet Engine process required for single-node operation.
- Linux x64 sidecar packages (@rivet-dev/agentos-sidecar-linux-x64-gnu)
  are available as optional dependencies.

Docker / Orb boundary:
- Docker Engine installed and zopu user in docker group.
- No Docker-backed sandbox code wired; Orb lane contract not yet landed.
- Volume pruning omitted from docker-cleanup.sh to protect durable data.

Validated: bash -n on all 6 shell scripts; mocked health-check smoke
(nc-based TCP probes, mocked systemctl/docker); systemd unit structural
checks. No JS/TS/agent files changed.

deploy/zopu-runtime/scripts/rollback.sh

@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+#
+# rollback.sh — Roll back to the previously deployed commit.
+#
+# Usage:
+#   rollback.sh              # roll back to .last-deployed-sha
+#   rollback.sh <sha>        # roll back to a specific commit
+#
+# .env is gitignored and is never touched by git operations. It survives
+# updates and rollbacks unchanged.
+
+set -euo pipefail
+
+INSTALL_DIR="${ZOPU_INSTALL_DIR:-/opt/zopu}"
+SERVICE_USER="${ZOPU_SERVICE_USER:-zopu}"
+
+GREEN='\033[0;32m'
+RED='\033[0;31m'
+NC='\033[0m'
+
+log() { echo -e "${GREEN}[rollback]${NC} $*"; }
+err() { echo -e "${RED}[rollback]${NC} $*" >&2; }
+
+cd "$INSTALL_DIR"
+
+# Determine target
+ROLLBACK_SHA="${1:-}"
+if [[ -z "$ROLLBACK_SHA" ]]; then
+  LAST_SHA_FILE="${INSTALL_DIR}/.last-deployed-sha"
+  if [[ ! -f "$LAST_SHA_FILE" ]]; then
+    err "No previous deployment recorded in ${LAST_SHA_FILE}."
+    err "Pass a commit SHA explicitly: rollback.sh <sha>"
+    exit 1
+  fi
+  ROLLBACK_SHA=$(cat "$LAST_SHA_FILE")
+fi
+
+# Validate commit exists
+if ! git rev-parse --verify "${ROLLBACK_SHA}^{commit}" &>/dev/null; then
+  err "Commit ${ROLLBACK_SHA} does not exist in the local repository."
+  exit 1
+fi
+
+CURRENT_SHA=$(git rev-parse HEAD)
+log "Current: ${CURRENT_SHA:0:12}"
+log "Rolling back to: ${ROLLBACK_SHA:0:12}"
+
+# Save current state before rolling back (enables re-rollback)
+echo "$CURRENT_SHA" > "${INSTALL_DIR}/.pre-rollback-sha"
+
+# Checkout target
+git checkout "$ROLLBACK_SHA"
+
+# Confirm .env is intact
+if [[ -f "${INSTALL_DIR}/.env" ]]; then
+  log ".env preserved."
+else
+  err ".env is missing! Restore it from backup before starting services."
+fi
+
+log "Running bun install..."
+sudo -u "$SERVICE_USER" bun install
+
+log "Building daemon..."
+sudo -u "$SERVICE_USER" bun run build:daemon
+
+log "Building agent service..."
+sudo -u "$SERVICE_USER" bun run build:agents
+
+log "Restarting services..."
+systemctl restart zopu-daemon
+sleep 3
+systemctl restart zopu-agent
+sleep 5
+
+# Health check
+HEALTH_SCRIPT="${INSTALL_DIR}/deploy/zopu-runtime/scripts/health-check.sh"
+if [[ -x "$HEALTH_SCRIPT" ]]; then
+  log "Running health check..."
+  if "$HEALTH_SCRIPT"; then
+    log "Rollback complete and healthy."
+  else
+    err "Health check failed after rollback!"
+    err "  journalctl -u zopu-daemon -n 50"
+    err "  journalctl -u zopu-agent -n 50"
+    exit 1
+  fi
+fi