feat(ci): add post-deploy smoke test pipeline stage

- Add scripts/smoke-test.sh — hits health, readiness, and critical API
  endpoints (listings, search, subscriptions) post-deploy
- Add smoke-test-staging job that runs after staging deploy with Slack
  notification on failure
- Add smoke-test-production job that runs after production deploy with
  success notification
- Add rollback-production job triggered on smoke test failure — reverts
  to previous container images and notifies via Slack

Co-Authored-By: Paperclip <noreply@paperclip.ing>

scripts/smoke-test.sh

@@ -0,0 +1,69 @@
+#!/usr/bin/env bash
+# Post-deploy smoke test — validates critical API endpoints after deployment.
+# Usage: ./scripts/smoke-test.sh <base-url> [timeout-seconds]
+# Exit codes: 0 = all checks pass, 1 = one or more checks failed
+
+set -euo pipefail
+
+BASE_URL="${1:?Usage: smoke-test.sh <base-url> [timeout-seconds]}"
+TIMEOUT="${2:-5}"
+FAILED=0
+TOTAL=0
+
+# Remove trailing slash
+BASE_URL="${BASE_URL%/}"
+
+smoke() {
+  local name="$1"
+  local method="${2:-GET}"
+  local path="$3"
+  local expected_status="${4:-200}"
+
+  TOTAL=$((TOTAL + 1))
+  local url="${BASE_URL}${path}"
+
+  local status
+  status=$(curl -s -o /dev/null -w "%{http_code}" -X "$method" \
+    --max-time "$TIMEOUT" "$url" 2>/dev/null) || status="000"
+
+  if [ "$status" = "$expected_status" ]; then
+    echo "  PASS  $name ($method $path) -> $status"
+  else
+    echo "  FAIL  $name ($method $path) -> $status (expected $expected_status)"
+    FAILED=$((FAILED + 1))
+  fi
+}
+
+echo "========================================"
+echo " Smoke Tests — $(date -u +%Y-%m-%dT%H:%M:%SZ)"
+echo " Target: $BASE_URL"
+echo "========================================"
+
+echo ""
+echo "--- Health & Readiness ---"
+smoke "Liveness probe"          GET "/health"
+smoke "Readiness probe"         GET "/ready"
+
+echo ""
+echo "--- Core API Endpoints ---"
+smoke "List listings"           GET "/listings"
+smoke "Search"                  GET "/search?q=test"
+smoke "Geo search"              GET "/search/geo?lat=10.8&lng=106.6&radius=5"
+smoke "Subscription plans"      GET "/subscriptions/plans"
+
+echo ""
+echo "--- Auth (expected responses) ---"
+smoke "Login (no body -> 400)"  POST "/auth/login" 400
+
+echo ""
+echo "========================================"
+echo " Results: $((TOTAL - FAILED))/$TOTAL passed"
+if [ "$FAILED" -gt 0 ]; then
+  echo " STATUS: FAILED ($FAILED failures)"
+  echo "========================================"
+  exit 1
+else
+  echo " STATUS: ALL PASSED"
+  echo "========================================"
+  exit 0
+fi