Release release-20260424181327-02622e8

Add fog of war feature

- Fog of war toggle via 'F' key (host/server only)
- New packet type 13 for fog state broadcast
- Radius-based visibility (300px) around local player
- Fog overlay with dark circles around visible entities
- Moving obstacles, bullets, and remote players hidden beyond radius
- Static obstacles always visible
- HUD indicator when fog is enabled