- Add 9 extended fields to AgentTemplateInfo: soul_content, scenarios,
welcome_message, quick_commands, personality, communication_style,
emoji, version, source_id
- Refactor service.rs to use sqlx::Row (manual column extraction) to
avoid the 16-element tuple FromRow limit
- Add /api/v1/agent-templates/available (lightweight public listing)
and /api/v1/agent-templates/:id/full endpoints
- Add 24h key_usage_window cleanup task in scheduler
- Update seed data with extended fields for all 5 existing templates
plus new Medical Assistant template (healthcare category)
