refactor(jwt): gate signing-key auto-rotation cron on SIGNING_KEY_ROTATION_DAYS (#20866)

Only register the JWT signing-key rotation cron when
`SIGNING_KEY_ROTATION_DAYS` is set, and move that variable to Advanced
Settings.

packages/twenty-server/src/engine/core-modules/twenty-config/config-variables.ts

@@ -1185,9 +1185,9 @@ export class ConfigVariables {
   FALLBACK_ENCRYPTION_KEY: string;
 
   @ConfigVariablesMetadata({
-    group: ConfigVariablesGroup.SERVER_CONFIG,
+    group: ConfigVariablesGroup.ADVANCED_SETTINGS,
     description:
-      'Number of days after which the Enterprise auto-rotation cron issues a new current JWT signing key. When unset, the cron is a no-op. Previous keys remain in the database to keep verifying tokens they signed; revocation stays a manual admin action.',
+      'Days the current JWT signing key stays valid before the rotation cron issues a new one. Leave unset to disable auto-rotation.',
     type: ConfigVariableType.NUMBER,
   })
   @CastToPositiveNumber()