feat(security): harden the API, trust Hiboutik for deletions, lock syncs (#3)

- Sync deletions: a 2xx Hiboutik answer is the truth, even an empty list; a failed call (HTTP error or non-list body) deletes nothing (HiboutikClient.getList).
- Validate the environment at startup (HIBOUTIK_BASE_URL must be HTTPS), global ValidationPipe, Helmet, CORS opt-in, HTTP timeouts, rate limiting (60 req/min/IP, 5 on POST /sync), AllExceptionsFilter.
- Postgres advisory lock so only one synchronization runs at a time across instances; syncAll is private, syncs start through startSync.
- Fix the Jest moduleNameMapper; document the validation and security rules in CLAUDE.md.

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"
   }
 }