feat(setup): Stage 1 first-time setup wizard backend (no UI)

Task #534 — backend, infra, tooling. UI ships in Stage 2 (#535).

Backend
- New system_settings table (id=1 singleton): installed flag, base_url,
  local_domain, local_ip, https_mode, app_version. Pushed to dev DB.
- New /api/setup/status (open) and /api/setup/{validate,complete}
  (gated by requireSetupOpen — 409 once installed).
- completeInstall is fully transactional: pg_advisory_xact_lock
  serializes concurrent callers, double-gates on installed flag and
  admin existence, then atomically creates the admin user, assigns
  admin role + Admins/Everyone groups, and flips system_settings to
  installed=true. Rolls back on any failure.
- Added redirectIfSetupNeeded() helper returning the full SetupStatus
  payload alongside a redirect target for SPA routing decisions.
- Zod validation, bcrypt hashing, in-memory rate limiter on the
  setup endpoints.

Backward compat
- scripts/src/seed.ts now branches on installed flag + admin
  existence + SEED_*_PASSWORD env vars. Legacy installs (admin
  exists, system_settings empty) get backfilled to installed=true
  via ON CONFLICT DO UPDATE so they are never forced through the
  wizard. When env passwords are unset and no admin exists, the
  seed prints a wizard hint instead of seeding.

Infra
- docker-compose.yml: replaced nginx edge with a Caddy service that
  mounts ./certs and ./docker/Caddyfile{,.skip}. The web service no
  longer publishes a port directly — Caddy is the only public ingress.
- Caddy entrypoint picks Caddyfile.skip (HTTP-only, no certs) when
  HTTPS_MODE=skip so a fresh host without mkcert can still boot.
- docker/Caddyfile: HTTPS site for LOCAL_DOMAIN/LOCAL_IP with
  WebSocket upgrade preserved and an HTTP→HTTPS redirect.
- start.sh: preserved. Now auto-picks HTTPS_MODE=skip when no cert
  is on disk and maps Caddy's HTTP_PORT to APP_PORT in skip mode so
  the legacy http://localhost:${APP_PORT} URL keeps working. In
  local/byo mode it prints the https://${LOCAL_DOMAIN} URL.
- .env.example: added LOCAL_DOMAIN, LOCAL_IP, BASE_URL, HTTP_PORT,
  HTTPS_PORT, HTTPS_MODE; SEED_*_PASSWORD now optional.

Tooling
- scripts/local-setup.sh: idempotent OS-aware bootstrap (.env upsert,
  mkcert hint, cert SAN check, dry-run via LOCAL_SETUP_DRY_RUN).

Tests
- artifacts/api-server/tests/setup-wizard.test.mjs: 7/7 pass.
- scripts/tests/local-setup.test.mjs: 2/2 pass.

Constraints honored: no force-push, no destructive ops, start.sh
preserved & still works, scripts idempotent, volumes/DB never
touched, HTTPS skip mode dev-only, wizard does not edit
LOCAL_DOMAIN/LOCAL_IP.

Out of scope / not addressed: pre-existing TS errors in
routes/users.ts and pre-existing failure in
executive-meetings-postpone-race.test.mjs.

scripts/local-setup.sh

@@ -209,7 +209,23 @@ env_set LOCAL_DOMAIN "$LOCAL_DOMAIN"
 env_set LOCAL_IP     "$LOCAL_IP"
 env_set BASE_URL              "https://$LOCAL_DOMAIN"
 env_set PUBLIC_BASE_URL       "https://$LOCAL_DOMAIN"
-env_set ALLOWED_ORIGINS       "https://$LOCAL_DOMAIN,https://$LOCAL_IP"
+# Merge — never overwrite — ALLOWED_ORIGINS so operator-added origins
+# (e.g. a Tailscale name, an extra LAN IP) are preserved across re-runs.
+EXISTING_ORIGINS="$(env_get ALLOWED_ORIGINS)"
+NEW_ORIGINS="https://$LOCAL_DOMAIN,https://$LOCAL_IP"
+MERGED_ORIGINS="$NEW_ORIGINS"
+if [ -n "$EXISTING_ORIGINS" ]; then
+  IFS=',' read -r -a _existing_arr <<< "$EXISTING_ORIGINS"
+  for o in "${_existing_arr[@]}"; do
+    o="$(printf "%s" "$o" | sed -e 's/^ *//' -e 's/ *$//')"
+    [ -z "$o" ] && continue
+    case ",$MERGED_ORIGINS," in
+      *",$o,"*) ;;  # already present
+      *) MERGED_ORIGINS="$MERGED_ORIGINS,$o" ;;
+    esac
+  done
+fi
+env_set ALLOWED_ORIGINS       "$MERGED_ORIGINS"
 # Default HTTPS_MODE to "local" only if not already set (preserves byo/skip).
 if [ -z "$(env_get HTTPS_MODE)" ]; then
   env_set HTTPS_MODE "local"