feat(compose): full-stack Caddy + docker-compose wiring

Brings up the whole platform behind a single Caddy entrypoint so the
routing topology can be exercised end-to-end before any feature code
lands. Same Caddyfile shape (admin / data plane / dashboard) maps to
single-process MVP today and will map to cluster mode later by
swapping the upstream lists, not by restructuring the proxy.

  * caddy/Caddyfile — dev: HTTP only, picloud and dashboard upstreams
    by service name. caddy/Caddyfile.prod — Let's Encrypt for
    PICLOUD_DOMAIN with PICLOUD_ADMIN_EMAIL.
  * docker/orchestrator.Dockerfile — multi-stage build of the
    `picloud` all-in-one against the pinned 1.92 toolchain; debian
    slim runtime, non-root user, /healthz HEALTHCHECK.
  * docker/dashboard.Dockerfile — node:24-alpine builder + caddy
    runtime that serves the static SPA with SPA fallback.
  * docker-compose.yml — postgres + picloud + dashboard + caddy,
    Caddy exposed on host :8000 (configurable), Postgres on :15432
    (loopback only). Health-gated startup ordering.
  * docker-compose.prod.yml — overlay: removes Postgres host
    mapping, expands Caddy to 80/443/443udp, swaps Caddyfile.prod,
    adds restart policy.
  * .env.example documents every knob the compose stack reads.

Verified via `docker compose up -d`:
  * `curl :8000/healthz` → 200 ok (orchestrator)
  * `curl :8000/api/admin/scripts` → 404 (manager, routed correctly)
  * `curl :8000/api/execute/<id>` → 404 (orchestrator, routed correctly)
  * `curl :8000/` → SPA index served (dashboard via Caddy)
  * `curl :8000/favicon.svg` → 200 image/svg+xml
  * Postgres healthy and reachable on 127.0.0.1:15432.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker-compose.prod.yml

@@ -0,0 +1,39 @@
+# Production overlay. Apply on top of docker-compose.yml:
+#
+#   docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d
+#
+# Pre-flight checks:
+#   - PICLOUD_DOMAIN and PICLOUD_ADMIN_EMAIL must be set (Caddy uses them
+#     for automatic Let's Encrypt issuance).
+#   - POSTGRES_PASSWORD must be set to a real secret, not the dev default.
+
+services:
+  postgres:
+    # Pull the published port mapping; Postgres is reachable only inside
+    # the compose network in production.
+    ports: !reset []
+    restart: unless-stopped
+
+  picloud:
+    restart: unless-stopped
+    environment:
+      RUST_LOG: ${RUST_LOG:-info,picloud=info}
+
+  dashboard:
+    restart: unless-stopped
+
+  caddy:
+    # Swap the dev Caddyfile for the prod one, expose 80/443, pass the
+    # domain + admin email through for Let's Encrypt.
+    volumes:
+      - ./caddy/Caddyfile.prod:/etc/caddy/Caddyfile:ro
+      - caddy_data:/data
+      - caddy_config:/config
+    ports: !override
+      - "80:80"
+      - "443:443"
+      - "443:443/udp"
+    environment:
+      PICLOUD_DOMAIN: ${PICLOUD_DOMAIN}
+      PICLOUD_ADMIN_EMAIL: ${PICLOUD_ADMIN_EMAIL}
+    restart: unless-stopped