Reorganize HandleNodeFromAuthPath (~300 lines) into a cleaner structure
with named conditions and extracted helper functions.
Changes:
- Add authNodeUpdateParams struct for shared update logic
- Extract applyAuthNodeUpdate for common reauth/convert operations
- Extract reauthExistingNode and convertTaggedNodeToUser handlers
- Extract createNewNodeFromAuth for new node creation
- Use named boolean conditions (nodeExistsForSameUser, existingNodeIsTagged,
existingNodeOwnedByOtherUser) instead of compound if conditions
- Create logger with common fields (registration_id, user.name, machine.key,
method) to reduce log statement verbosity
Updates #3038