Updates an existing system. All request body fields are optional — only supplied
fields are applied. The system's type cannot be changed via this endpoint.

If system.components is omitted, the system's existing components are left unchanged.
If system.components is present, it is authoritative: the submitted array is treated
as the desired final component set, and existing components omitted from the array are removed.

Component matching behavior for components[] entries:

1. Match by id — if a payload supplies an id, the component with that id is updated.
2. Fallback to typeCode — if no id is supplied (or the id is not found), the system's
   existing components are searched by typeCode. The fallback only applies when exactly
   one existing component matches; if multiple components share the same typeCode the
   entry is skipped (ambiguous — supply id to disambiguate).
3. New component creation — if no existing component matches and the typeCode is a valid
   component type code, a new component is created.
4. Unknown typeCode — if no existing component matches and the typeCode does not
   correspond to a known component type, the entry is silently skipped.