feat(quality): Sprint 2 pre-deploy gates and server smoke tests

Extract Express app factory for testability, add Vitest/Supertest API
smoke tests, root npm run check script, and deployment docs. Fix
express-rate-limit IPv6 keyGenerator for feedback limiter.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/predeploy-check.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+# Local quality gates before deploying to kapteins-daagbok.eu (no external CI).
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$ROOT"
+
+echo "=================================================="
+echo "  Kapteins Daagbok — pre-deploy checks"
+echo "=================================================="
+
+run() {
+  echo ""
+  echo "==> $*"
+  "$@"
+}
+
+run npm run validate:i18n
+
+pushd client >/dev/null
+if [ ! -d node_modules ]; then
+  run npm ci
+fi
+# Lint: run separately with `npm run lint` (client ESLint; cleanup tracked separately)
+run npm run test
+run npm run build
+popd >/dev/null
+
+pushd server >/dev/null
+if [ ! -d node_modules ]; then
+  run npm ci
+fi
+run npm run test
+run npm run build
+popd >/dev/null
+
+echo ""
+echo "=================================================="
+echo "  All pre-deploy checks passed."
+echo "=================================================="