feat(backend): add operational smoke tooling and safe pricing cleanup endpoints

- add backend README and refresh API map and smoke regression docs
- add full backend smoke regression script
- add admin pricing cleanup preview and dry-run endpoints
- add helper script for test pricing cleanup
- verify typed error contracts, draft flow, publish readiness and preview flows
- verify publish preview retention and clean backend startup behavior

backend/scripts/cleanup_test_pricing_data.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+API_URL="${API_URL:-http://127.0.0.1:9020}"
+API_KEY="${API_KEY:-admin-local-dev-key}"
+SCHEME_ID="${SCHEME_ID:-}"
+DRY_RUN="${DRY_RUN:-true}"
+
+if [[ -z "${SCHEME_ID}" ]]; then
+  echo "SCHEME_ID is required"
+  exit 1
+fi
+
+REQUEST_BODY=$(cat <<JSON
+{
+  "code_prefixes": ["FAIL_", "DIAG_", "AUTO_", "TYPED_"],
+  "name_prefixes": ["should-fail-", "diag-", "auto ", "typed-response-"],
+  "pricing_category_ids": [],
+  "delete_only_without_rules": true,
+  "dry_run": ${DRY_RUN}
+}
+JSON
+)
+
+echo "===== CLEANUP PREVIEW ====="
+curl -sS \
+  -H "X-API-Key: ${API_KEY}" \
+  "${API_URL}/api/v1/admin/schemes/${SCHEME_ID}/pricing/categories/cleanup-preview?code_prefix=FAIL_&code_prefix=DIAG_&code_prefix=AUTO_&code_prefix=TYPED_&name_prefix=should-fail-&name_prefix=diag-&name_prefix=auto%20&name_prefix=typed-response-" \
+| python3 -m json.tool
+
+echo
+echo "===== CLEANUP EXECUTE (DRY_RUN=${DRY_RUN}) ====="
+curl -sS -X POST \
+  -H "Content-Type: application/json" \
+  -H "X-API-Key: ${API_KEY}" \
+  -d "${REQUEST_BODY}" \
+  "${API_URL}/api/v1/admin/schemes/${SCHEME_ID}/pricing/categories/cleanup" \
+| python3 -m json.tool