Function mergeServerExtensionConfigs

Merge Open App–discovered extension configs with the host mj.config.cjs list.

• Identity is DriverClass.
• Later discovered entries replace earlier ones (ClassFactory last-wins).
• Host overlay wins Enabled and RootPath when the host provides them; Settings is { ...discovered, ...host }.
• Host-only DriverClasses append after discovered ones.
• A host Enabled: false entry is kept so the loader skips that DriverClass rather than falling back to the discovered one.