Add a Persona

Creates reusable, composable system prompt definitions with template variables and a global registry.

Before Starting

Ask the user for:

Persona name (lowercase_with_underscores, used as registry key)
Purpose — what the persona should do (extract data, analyze, summarize, etc.)
System prompt — the core instruction text
Template variables — any {{variable}} placeholders and their defaults
Constraints — rules the persona must follow
Model hint — suggested model string (optional, e.g. "openai/gpt-4o")
Settings — default driver options (optional, e.g. {"temperature": 0.0})