- Add three navigation modes cycled with V key: walk (WASD + mouse look),
orbit (drag to rotate around focal point, scroll to zoom, WASD to pan),
fly (WASD + Q/E for vertical, mouse look, unconstrained movement)
- Camera rig syncs between modes for smooth transitions
- Performance tier detection: low (mobile, no shadows, 25% particles),
medium (<8 cores, 1.5x DPR, 60% particles), high (M3 Max, 2x DPR, 2048 shadows)
- Shadow map resolution scales with tier (2048/1024/512)
- Nav mode displayed in HUD controls bar with gold highlight
Fixes#4