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/setup-env.ts

@@ -0,0 +1,5 @@
+// The e2e test needs neither a database nor Hiboutik, but the app validates its environment at startup: provide dummy values.
+process.env.DATABASE_URL ??= 'postgresql://test:test@localhost:5432/test';
+process.env.HIBOUTIK_BASE_URL ??= 'https://example.hiboutik.test/api';
+process.env.HIBOUTIK_USERNAME ??= 'test';
+process.env.HIBOUTIK_PASSWORD ??= 'test';