Add three documentation pages:
- Leden vs Personen: explains the difference between platform members and event participants
- Crowd Types: full reference for the 7 person types with access matrix
- Diensten plannen: enhanced with 4-layer model, assignment strategies, and overbezetting
Also adds placeholder images to fix VitePress build and updates sidebar navigation.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
