Make output field explicit for all insights, remove frequency check
Add explicit "output": "md" to all insights that produce markdown files.
speakers.md keeps "output": "json". Hook-only prompts (occurrence,
anticipation) and special cases (importer) have no frequency field.
Remove the frequency/mode mismatch validation in insight CLI, allowing
any prompt to be run directly by name regardless of --segment flag.
This enables using output+frequency as discriminators to differentiate
insights from agents when merging prompt directories.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>