Remove iq option from category config, use providers system
The iq field in category JSON was informational-only and didn't affect
model routing. All category follow-ups already use the providers config
system via observe.describe.* context pattern.
- Remove iq field from meeting.json and messaging.json
- Remove iq handling code from observe/describe.py
- Update docs and tests to reflect simplified schema
- Add note in SCREEN_CATEGORIES.md pointing to providers config
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>