Make tools field explicit for all agents, remove implicit default
Add explicit "tools": "default" to agents that were relying on the
implicit fallback (decisionalizer, doctor, joke_bot). Remove the
automatic default tool pack assignment in cortex.py and cli.py.
This enables using the tools field as a discriminator to differentiate
agents from insights when merging prompt directories.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>