Add tone adjustment controls for AI-generated content

[jeffpaul]

Explore adding tone or style controls (for example: casual, formal, technical) to AI-generated and AI-rewritten content in the editor. This would allow users to guide the voice of generated text without manual prompt editing.

This should be designed as an experiment and built on top of existing Abilities and prompt infrastructure.

Acceptance criteria:

• Define supported tone options and how they are selected in the UI
• Tone selection influences AI output consistently
• Implementation works across relevant editor experiments
• Extensible for additional tones or styles in the future