feat(security): harden the API and lock synchronizations across instances

- Validate the environment at startup (src/config): required variables
  must be present, HIBOUTIK_BASE_URL must be HTTPS.
- Global ValidationPipe (whitelist, forbidNonWhitelisted, transform).
- Helmet, CORS disabled unless CORS_ORIGINS is set, TRUST_PROXY support,
  HTTP header/request timeouts, shutdown hooks.
- Rate limiting: 60 req/min/IP globally, 5 req/min on POST /sync.
- AllExceptionsFilter: unexpected errors are logged (message + stack,
  never the raw error object) and answered with a generic 500.
- Postgres advisory lock (dedicated connection) so only one
  synchronization runs at a time across all instances; released by
  Postgres itself if the process dies.
- Fix the Jest moduleNameMapper (unescaped dot also matched .cjs files).
- Document the input validation and security rules in CLAUDE.md.
- Add class-validator, class-transformer, helmet and @nestjs/throttler;
  npm audit fix refreshed package-lock.json.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

test/jest-e2e.json

@@ -3,6 +3,7 @@
   "rootDir": ".",
   "testEnvironment": "node",
   "testRegex": ".e2e-spec.ts$",
+  "setupFiles": ["<rootDir>/setup-env.ts"],
   "transform": {
     "^.+.ts$": "ts-jest",
     "^.+.js$": [
@@ -18,6 +19,6 @@
   },
   "transformIgnorePatterns": ["/node_modules/(?!@nestjs/config/)"],
   "moduleNameMapper": {
-    "^(.{1,2}/.*).js$": "$1"
+    "^(\\.{1,2}/.*)\\.js$": "$1"
   }
 }