Add unit tests for ChangesHelper methods

[fusion94]

Description

ChangesHelper has no dedicated specs. Methods like changes_for, change_title_for, change_item_types, text_or_nil, and version_reify are untested in isolation.

Acceptance Criteria

• changes_for tested for create, update, and destroy events
• changes_for tested with nil changeset
• change_title_for tested with and without item_name_method
• change_item_types returns sorted list of versioned models
• text_or_nil returns <em>nil</em> for nil, escaped text otherwise
• version_reify rescues ArgumentError gracefully