fix(deploy): package-lock.json versionieren für npm ci

- Zeile **/package-lock.json aus .gitignore entfernt; Locks zu backend,
  frontend und Repo-Root hinzugefügt, damit Deploy-Skripte mit npm ci
  dieselben Versionen wie package.json installieren.
- backend: Script lockfile:sync und Hinweis in description.

Made-with: Cursor

backend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "backend",
   "version": "1.0.0",
-  "description": "",
+  "description": "Nach Änderungen an dependencies: npm install ausführen und package-lock.json committen (npm ci im Deploy).",
   "type": "module",
   "main": "index.js",
   "scripts": {
@@ -14,6 +14,7 @@
     "cleanup-connections": "node cleanup-connections.js",
     "diag:town-worth": "QUIET_ENV_LOGS=1 DOTENV_CONFIG_QUIET=1 node scripts/falukant-town-product-worth-stats.mjs",
     "diag:moneyflow": "QUIET_ENV_LOGS=1 DOTENV_CONFIG_QUIET=1 node scripts/falukant-moneyflow-report.mjs",
+    "lockfile:sync": "npm install --package-lock-only",
     "test": "echo \"Error: no test specified\" && exit 1"
   },
   "keywords": [],