Clarify and consolidate Title Generation options in UI and Experiment settings

What problem does this address?

Following on from #10, the Title Generation experiment needs clearer definition around where and how its generation options are exposed. The current design shows a dropdown menu attached to the “Generate” button in the post editor, allowing users to choose between different title generation modes. At the same time, we could expose these options as configurable in the AI Experiments settings, or offering both approaches.

This issue aims to determine the right balance:

• Should users control these options only from the in-editor dropdown?
• Should the experiment setting define defaults or preferred modes?
• Should both exist and complement each other?

Key questions:

• What specific generation modes should the dropdown include? Current options are "Sentence case" and "Title case". Are there others to consider? Do these "make sense" in non-English languages?
• Should the dropdown override experiment-level settings or inherit them?
• Should experiment settings define default behavior for the dropdown?
• How do we keep the UI simple while still offering advanced control?

What is your proposed solution?

Proposal:

• Review the design for the in-editor Title Generation dropdown.
• Explore adding experiment-level configuration for default mode selection.
• Align behaviors so editor actions and experiment settings do not conflict.

Design reference: